Honestly at this point I would like to see the reset button.
I want to see them remake WoW starting fresh with a level cap of 20 or 40 and a completely re-imagined world using a new engine. Nothing brought over from the old game.
It would let them go back and re-tell the story of WoW from the beginning the right way and not having to support all the old stuff would not only be liberating but inject new energy into what has become an old game that I'm sure developers find a PITA to work on when they could do so much better.
More importantly it would open WoW up to new players who feel like it's daunting to deal with 100 levels AND log on and think the game is some relic from the 20th century when they look at most of the starting zones. The refresh for Cataclysm helped A LOT but it's just not enough anymore. WoW looks VERY dated until you hit the post- Cataclysm content.
I really want to experience the old story arcs again in a re-imagined form and the Warcraft movie and WoD give Blizzard the perfect opportunity to do just that. I think the next few expansions will feel forced and kind of lame if they don't make the change now.
In terms of the general feeling of WoD and what I would want to see in a new expansion (or ideally a reboot):
5-man dungeons need to be a central focus again:
A lot of MMOs were based on the Asian model of giant raids and very large groups but Americans are not really wired that way. We prefer small groups of close friends and that's usually how things end up. The idea of 20-man or 40-man raids sounds epic in theory but some of the most satisfying gameplay I've experienced in WoW has been small group content that they were able to make more challenging because you don't need to manage a group of 20 people. I think a good number of 5-mans to shoot for at launch is between 8 and 10. The group finder for the traditional style of 5-man that we currently have is fine. But I would also like to see another level. Challenge Mode and Mythic 5-mans are the wrong approach IMHO. It's not really that fun to try and speed run content (and the pressure of doing so is destructive to groups) and just cranking up the numbers for a 5-man to be harder is lame and feels recycled. What I want are essentially 5-man raids ... 5-man content designed for a 2-3 hour clear and no dungeon finder. Not as a replacement to the current 5-man model but as something you add on as the next step in progression. Just 1 or 2 of these per patch would be fine. Keeping 10 and 20 man raids in the game would be fine too but they should keep the same group composition of 1 tank 1 healer and 3 DPS for every 5 people. By designing 20-man raids that need 2 tanks you create the lack of tanks problem so just avoid that. The large raids and 5-man raids should be complementary to each other in terms of progression. They should reward the same item level gear for a tier and just be treated as additional raids (otherwise there is no reason to do them).
Return of point-based reward systems:
Along with 5-man content and the Dungeon Finder JP and VP work very well and were a part of what helped WoW be so popular in WotLK. For WoD the gearing experience ranges from annoying to incredibly frustrating as you can literally be screwed over by the randomness of trying to get gear. This has the effect of making players ask "what is the point" when thinking about doing something because the chance they'll get what they need is very low and it doesn't FEEL like they're making progress on it. It also has the problem of KILLING replay value of content. After you got the gear you needed from 5-mans they were effectively dead and you never went back to them. This is because there is no good reason to do so. With the traditional point-based reward systems like JP and VP there was a GOOD reason to run 5-mans throughout the course of an expansion and there was enough variety in the number of 5-mans that it didn't get old. There always needs to be something that makes the player feel like they aren't wasting their time and the WoD model has forgotten that. Once this currency is in place it's easy to create reasons to want to do it even after you have the gear you need (you can have a vendor that converts the points into useful crafting mats or have some big ticket items to strive for like special mounts and pets).
Bring back mindless daily quests:
People complained a bit about the daily quest grind in MoP and to some extent I agree because they were used to gate access to things you felt obligated to get for raiding. But the daily quests themselves weren't bad. It was the fact that people were forced to do them. A LOT of people like just having 30 min or an hour of things to do each day that doesn't require thought but will provide you a benefit (making gold being the most important). I might be relatively alone on this one but I actually LOVED all the daily quests in MoP. It made me feel like I was making progress on my character but didn't require a lot of attention or research. Just something to do if I have the time and a reason to log in each day. I did NOT like the grind of the Timeless Isle. Catch-up gear is better introduced through new 5-mans and crafted BoEs. I also like the structure of daily quests. Do X get Y and once you're done you're done. You don't struggle with yourself if you should keep going or not. You don't feel obligated to do 4-5 hour grind sessions. Anyway ... my point is bring back daily quest hubs.
Make the Legendary account-wide:
I like the experience of the Legendary quest and it feels great. BUT it also has the effect of forcing you to abandon your alts. Even if you get your alts to max level the daunting grind of a Legendary quest chain (which IS required for raiding let's not kid ourselves) makes you have no desire to play alts. This has a huge impact on WoW feeling like there is a lack of content because I'm now restricted to experiencing that content with one character so of course it feels like the game is old. Back in Cataclysm I was able to maintain 10 toons that were at max level and geared enough to bring along to a raid. For MoP and WoD the Legendary requirement made me give up after trying to get a 2nd toon going. Also the lack of point-based rewards in 5-mans meant I couldn't just work on gearing those toons up easily by having friends run 5-mans with me which takes away a social opportunity.
Say NO to garrisons:
Garrisons were a cool leveling experience and they felt cool for the first week or two but the cost of that was the game now feels EMPTY. The farm in MoP was OK as a personal thing but the Garrison is too much of a time sink and keeps people too isolated. I don't feel like I've enjoyed WoD more because of Garrisons and the amount of complexity to them is just something I don't care about. I'm fine investing time to learn raid encounters out of game but don't make me start reading up on how to min max my garrison and require elaborate addons to be efficient at sending followers around. Ultimately I see Garrisons as a HUGE time sink and WASTE of development time. 6.1 was basically a patch for Garrisons. I would have rather had a 5-man or a new quest line with some story. The amount of time spent on the Shipyard for 6.2 just makes me roll my eyes. Garrisons are already old and adding ANOTHER garrison is not fun. Just stop.
Bring back smaller raids:
In addition to the "major" raid for the tier the short 1-boss raids that were available in WotLK need to come back. They're inexpensive to do and can be a fun way to meet people. If you have a rare drop like a mount attached it gives people a reason to try each week but not the end of the world if they don't have time. The open world raid bosses have somewhat replaced these but I don't think that's a good thing. The problem with the open world bosses is that you just throw yourself into the looking for group tool jump in and roll your face on the keyboard loot the boss and leave party. You don't meet anyone or establish friendships that way.
Eliminate LFR:
LFR cheapens the raid experience and does irreparable harm to the FEELING you get when you walk into a new wing of a raid for the first time or down a boss for the first time because it exposes that it's just a numbers game. The dungeon finder works because its based on 5-man groups and usually 2-3 of them know each other. 10 or 20 random people is too much which forces you to make the content a joke which makes it not fun. Just get rid of LFR please.
More story:
The storytelling in MoP (and even Cataclysm) was amazing. More of that please. I like the little RP quest lines sprinkled throughout the expansion to keep moving the story and add context to the raids. WoD had a very strong start but after you hit max level everything just stopped and the game feels dead. There should have been a minor content patch or two to introduce some new quest lines and maybe a 5-man or two.
Skill-based PvP:
Normalize gear for PvP so PvP isn't about getting better gear just about skill. The PvP rewards can be xmog sets, titles, and mounts that look AWESOME but we don't need PvP gear and we don't need new PvPers just having to suffer through being owned for weeks until they get enough gear to be half decent. If you want gear progression there is plenty of PvE content for that. PvP should be about player skill and the playing field should be fair.
I could go on... but I've already written a wall of text that nobody will read so I'll stop here :-)