Moltres get! All that is left is Articuno. With Yveltal in possession, I no longer need to get Pokemon Y. I'll continue to offer up Vivillon for the legendaries, even after I get Articuno. Will be a good idea for future in getting other legendaries from past games as well as forward thinking so for the next games down the road I have something good to offer.
Think I'll get Pokemon White or Black eventually. I previously played through Black 2 before I transferred my Pokemon X game and sold it off. So playing through Black/White 1 will give me a chance to get the legendaries from there. Also, that way I can eventually get HeartGold so that I can then transfer those Pokemon to White 1 and then to X.
Of course, getting more legendaries from Vivillon trades will of course make the above not really necessary.
Trust me, evolving at least a bunch of them now, whenever convenient, helps a lot when going for the gold.
Oh yeah. I still plan to catch and evolve all Pokemon. I'm just currently skipping Pokemon who's entire evolution line I've seen. Still evolving or catching/etc other Pokemon to get their line seen. Will of course come in handy when I eventually transfer these Pokemon to the next gen series. (not sure I'll transfer to Ruby 3DS/etc or use those Pokemon to transfer to X)