Monks are definitively underrepresented on the PTR, and it's always going to happen with weaker or even just less exciting builds. All the support builds as a whole were under-represented, and there wasn't that much testing going on when it comes to serious 4 man groups. For higher rifts the blinding flash globe gen monk is definitively going to be around, and I expect to see globe generating pull barbs as a staple as well. U6 has also been brought a lot closer to par when it comes to grift performance without being significantly improved for T10 farming, effectively putting it with the group there too. It isn't going to be topping any leaderboards, but it does feel like you're less likely to hear 'go back to solo/t10 noob' when bringing it to groups.
What was really hit was the SWK EP build (which was my best geared build last season), and the sc build. These were two builds that effectively dominated performance in their respective metas because of how their skill damage scales with density and with group synergy. There isn't really a way of making the current implementation of super high damaging skills that can be proced by others at the caster's damage scale nicely when compared to the types of skills other builds use.
The main let down isn't that these builds were nerfed, but the relative mediocrity of the new builds we got. The sweeping wind monk can be great at T10, it just isn't that good beyond that. The new pet builds are quite cool as well, but suffer from putting a lot of your damage into the hands of fumbling idiots that spend a significant portion of their time with their thumbs up their arse. Ultimately it looks like one of the strongest builds could be Quinn's pet build thingy, and with the inner sanctuary and mantras it isn't going to be playable at the really high group levels that would want a blinding flash monk. You also have to deal with the chest cramps that come with watching your DPS source sit there eating glue for a few seconds before deciding to attack.
I'm not going to be playing any monk on seasonal, but that said I will probably be messing around with it on non-season at least a little bit. And I don't think you will be too disappointed playing the class so long as your expectations aren't to be high on the leaderboards as a DPS in 2-4 player groups. And honestly, I'm really liking the way the new meta is looking without the million LPS heal monks of last season. Currently it's looking like most 4 player groups will be just as happy running grifts with random DPS characters from different classes as they will be having the 2 strongest demon hunters and two supports, and running a grift with two or three people isn't anywhere near as punishing. You also can't just stand around only worrying about things that will one shot you, counting on your support for everything else.
Monk isn't left out of the meta next season, it's just missing a strong DPS character for the group leaderboard levels of play.