But didn't Vigil get DS2 up and running on WiiU in a matter of weeks?
Yep. Really doesn't mean a lot though. RE6 is bound to be a big game. Capcom probably doesn't have the resources laying around to do a port that meets their quality standards without having to delay all the other versions out of the holiday window.
I've said it before and it bears repeating: I expect that we'll see most if not all the annual stuff this Fall. Anything else is anybody's guess but I fully expect some of the multiplatform stuff to miss launch window and maybe even not get ported at all. It'll get at least somewhat made up for with a few late ports and "exclusive" third party content.
This isn't anything to get all that bothered by, just depends on available manpower, budget, and the state of whatever middleware they're using at the time.
You can't in all fairness make any statements about the quality of third party support until maybe a year, year and a half after the system launches.