Melta I think may see a drop in trade for plasma. Especially for MEQ armies. With rapid fire changed, plasma can wipe tanks out from longer (safer) distances without suffering a potential 6" explosion.
Tanks, specifically rhinos used as mobile walls and to help units block characters and IC's from LOS so they can't look out sir wounds away. 35 points to help protect a squad of 150+ sounds like a good deal to me.
Dark Eldar now have the best anti tank units in the game IMHO. Wyches with haywire grenades. Multi assault out of a raider with haywire grenades against, who cares, glance those puppies to death. No explosions, no extra wounds and off you go.
Meta shift I see in people actually reading and knowing the rules and how to position their units. before it didn't matter, you just removed the guy you wanted. Now it really matters how you move units. Plus the rules aren't as forgiving to mistakes. In 5th ed people could troll around rules, get called out an it wasn't a big deal (sometimes). Now a foolish mistake can really mess you up. Like not reading how you can't assault out of transports. Now that will change as 6th ed becomes more saturated and people learn from mistakes. But even still, gotta be on top of what the rules say and do.
Lots more termies. Yes, I believe this is going to happen. I even broke down and bought some because of how wickedly awesome they are now. Especially BA termies. Hahahaha. *ahem. But seriously though, power weapons can't instagib them. They can instagib pretty much whatever with TH/SS. And they don't cost any more than last edition.
I really really think a nice thing about the meta is that it will actually begin to shift and change more than ever. With new combos, unusual mixes, and players realizing they have so much freedom to do things. Local meta will be changing and growing all the time. Tournament meta will probably be a set of things that are the most effective and efficient like 5th ed was. But on a more down to earth scale, playing with friends and random people. The meta will shift and grow as the game does. And that excites me. Not SPACE WOLVES are this, this and this forever!! (I play space wolves, this was an annoying problem) But with allies its so much more fun. Space Wolves and Orks (lawl), Blood Angels and Grey Knights (crap), eldar and dark eldar, so many more options to play the game is wonderful.