I agree as well, it wouldn't seem right if Luke turned to the dark side. Yes its been 30 years since Jedi but to me, personally it would be out of character. The OT would be all for nothing I think. Yeah it would make for a cool story/plot twist, but when Luke turned his lightsaber off and threw it to the side on the DSII - that was it. Luke overcame what Obi-wan and Yoda feared.
Even before all the leaked images, concept pics and even trailers came out, I always expected Luke to be the Obi-wan/Yoda of this trilogy.