Where there's Yveltal / Seismitoad, there is also Virizion / Genesect to fight the good fight and give them a run for their money, especially the Raichu variant. With Seismitoad, Night March, and Flareon decks losing a key card for recycling precious resources, VirGen may still be able to have a presence at Nationals and Worlds.... especially if Primal Groudon remains a player. Honely I think Mega Rayquaza can still make a splash, but it will require some restructuring. Keep and mind that everything I'm saying right now is about the current format and not once rotation hits. Running four copies of Sky Field will still allow RAyauza to win any Stadium war, and while discarding it will knock Pokemon off the field, most lists are already running Exeggcute PLF, which can be returned from the discard via its Propogation ability and re-benched after playing a new Sky Field. Ninetales PRC can also help, locking Sky Field in play. Losing Trump Card simply makes it a race for Rayquaza to take all of its prizes before decking out, because you will draw much of your deck during the first few turns. If you are able to score a KO every turn, that shouldn't be a difficult task, though it's certainly more easily said than done, especially if Garbodor returns to the scene.