Meta predictions? All I know is that Genji is as dead as Widow and McCree after their nerfs. I'm really curious to see what happens to support, will all of them bar Symmetra see some good play time?
If we're talking just everyone here, you might see less genjis and more hanzos but thats it. nothing huge. When it come to the pros, he wont get picked at all because in their world a "good enough" character is not enough. They need to squeeze every little bit of power out of a character and small weaknesses become huge for them.
In the pro world it's going to be reaper, mccree, tracer as the dps of choice. healers lucio for sure even with with nerf getting back faster to do engagements quicker to beat the clock will always be required but the second heal spot is going to be shared by zena nd mercy again depending on the situation and whether on attack or defence and the makeup of your team (maybe what the team feels better with), with zen slightly beating mercy in picks based on ult (it's better to stay alive and fight than die and be ressed).
Mei's buff is not going to change much for how much shes picked. She might get picked a little bit on koth matches but we'll see.
tanks it's going to be rein, zary, dva mostly with winston and hog maybe getting picked more when the opponents don't have a zen