If you want to raid in WoD....now is the time to get started.
Still plenty of time for people who are raiding right now to drop out (for whatever reason) and if you're there every week up to the expansion, that should say something. IMO, people are working on earning raid spots for Tier 17 right now. For most guilds they've got at least 14/14N down on farm if not well into heroics.
I think at this point the best credential you can have on your "resume" is at *minimum* a normal mode Garrosh kill. There are plenty of people making groups on places like Openraid and oQueue and all raids at all difficulties are cross-realm so I wouldn't say that would be super difficult. Heck, you could probably join in on a run and get asked if you're looking for a guild
But again, now is the time to start showing GMs and raid leaders who you are as a raider and person.