Dude, I just started here and we have beef already!?
Just kidding.
Anyway, I'm not too great at explaining the viability of decks in the meta; like why they would be good. But I will certainly try and if anyone has any other points, they are welcomed here.
1. The Serperior standard deck is an up-and-comer that is seeing more and more play since Fates Collide came out. If being a brand new deck, it's easy to see how someone might make a case for it to be sticking around. This deck, as well as most other decks, will be hurt by the loss of Battle Compressor (assuming it doesn't see a reprint), but alas, life goes on.
2. Strong Fight deck. Just like Serperior, this deck is brand new and it is already seeing tons of play. The loss of Korrina will be a detriment here but I believe this deck has enough stability that even losing amazing support like that, the combination of Zygarde/Regirock/Carbink is still too legit to quit. (Sorry)
3. M Alakazam EX. Once again, this is a brand new card that everyone was talking about even before it came out. Even if bats rotates out and does not see a reprint, it still has staying power on its own. The fact that you really don't actually need any other Pokemon besides Alakazam EX and it's mega form in a deck for it to compete (aside from Shaymin EX I suppose) is remarkable. But of course, you will still have help with Pokemon like Hoopa EX and Wobbuffett.
4. Yveltal has obviously been reprinted in Generations, and its EX counterpart has also just been reprinted in a new shiny skin. YZG is yet another deck that will be taking a huge blow by losing Battle Compressor (again, this is assuming that it rotates out and doesn't get reprinted) because the whole Maxie strategy is basically kaput. But I have been testing other "YZ" variations and still see success. I have even been seeing a few different Yveltal/Darkrai lists lately that have been working.
5. Ok, I'm not even sure of all the different Jolteon EX variants that are out there, but I think it's plentiful. XY11 will have a new Klefki card that looks fun to combine with Jolteon. But I'm not saying that will see success in any way. If XY base through Phantom Forces are rotating away (again, this is only speculation on my part), then Manectric EX will be going with it. But Jolteon still has some of its friends in Regice, Vileplume, and others who escape me at the moment.