In short there have been several times, especially in Return of the Jedi, that I felt Luke was already showing twinges of Dark....
And it is really interesting that there is that cut scene - I have always felt that when he turns up at Jabba's palace, there is more than a bit of the dark side about him. Look what he does to one of the guards as he goes in - Vader's throat grip.
He wears black throughout almost the entire film - a total 180 palate change from Empire, where he is still in the white/cream robes, even to the final scene.
In Return he is pretty much in black throughout.
I see a lot of potential for the dark side hanging around on the fringes with Luke, and I do think with the new film, the passage of time, that he may well have been thinking about the rights and wrongs of both sides - a kind of star based Third Way if you like.
It would certainly spice things up a bit. And they were left with a power vaccum at the top with both Vader and the Emperor gone...
(ticket for VII booked well in advance.....cannot wait)