I enjoy the meta game right now, and how old cards can come in to play in decks that feature cards from new expansions. Maybe I'm sensitive to change, but I like ranked as it is, and I hope it stays as competitive.

It will stay as competitive as it is atm, since you can still get legend in wild, a lot of people will keep on tryharding and netdecking in order to achieve it. I'm pretty sure sites like tempostorm will have now 2 different meta snapshots, one for standard and one for wild.

I assumed that most people would continue playing through Wild while newer players play Standard but I don't know anymore. They are totally different modes. What will the pros be playing?

That depends on their objective, if they solely wnat to achieve HCT points for blizzcon, they will most likely play standard over 80% of their time, if they wanna stream some weird shit decks, just like majordomo mage and funny stuff, that requires cards from wild, they will play some wild games on stream, I guess someone will dedicate a single day to streaming wild in order to keep all of their viewerbase there.

People who are more focused on casting, streaming and arena, will most likely play both formats around the same, since they may not have the need to get points for blizzcon.

Also we should have into consideration, that the meta is pretty much play aggro shit and hit the face, and many long term players have grown tired of this, and the current decks, so they may altogether just play standard only, in order to avoid shit like secret paladin and whatnot.

I also liked how I could work to fill out my collection, but with GVG packs being taken away, that goal is gone. Should I buy a bunch before they disappear?

That is pretty personal, if you are missing a lot of cards from GVG, and you are planning on playing wild, then go for it, because after that you will only be able to get them through dust and that's gonna be really expensive.

On the other hand if you are gonna play standard and you want to get cards from the new expanion as soon as possible in order to enjoy the new goodies, you should save up your gold. Also if you have like 90% of GvG cards for example, trying to get the ones you are missing (most likely epics and legendaries) through packs is pretty hard, statistically you would gain more non repeated new cards by buying the new packs and using the dust to craft what you are missing.

Since you can't buy specific cards in HS or trade like in other CCGs, the best way to obtain specific cards is through dust, and you get the same amount from dusting GvG and New expansion cards, so if you only want to craft epic and legendaries from GVG, waiting for the next expansion to spend your gold is the best choice.