Can't believe I missed this topic. Millennial voting patters are actually shaping up to be my specialty within academia and I recently conducted a survey study and wrote a 50ish page quant thesis using it, regarding issue importance and millennial voters.
Being a bit late to the party in here, there's a bit too much to be to just jump right into, but if there's anything people might be curious with specific questions I might be able to help. Far from me to claim to be an expert, but it was good enough the university paid to send me to a national research convention and pay for a fancy chart to go with my findings (which, in short, has parts that could point either way. Personally I wouldn't say a millennial shift is impossible, but the GOP would need to shift as well for it to happen)
I think, as a whole, technically, my fellow Millennials are trending Libertarian in their views, which could benefit the GOP, but possibly could not. I guess it would depend on whether those voters care more about social issues, which could lead them to supporting a Democrat, or if they care more about economic issues, which could lead them to supporting a Republican.