We might be able to write off Luke’s lines from the original trailer since they’re from ROTJ. They might not be repeated in TFA and could have just been used for a nostalgic effect in the trailer.
I don’t think Kylo Ren can be Luke just based on body shape and hair. The 2nd trailer shows the back of Ren’s head with Jon Snow style hair. Luke’s hair would be thinning by this time point. Ren seems to move like a younger man also.
The clincher for me though is Ren’s lightsaber because of how shoddy it is. Luke knew how to construct a functional lightsaber already. The only plausible way for it to be Luke is if he forgot the knowledge (unlikely) or lacked the resources to obtain the proper materials (and it looks like Ren has considerable resources). They’d also have to explain why he doesn’t have his old lightsaber.
Then again, Abrams turned Star Trek on it’s head, so you never know (or until December at least).