Well, he didn't own R2, and really wasn't around him all that much to remember him distinctly from any other astro droids, which were numerous.
Don't know about the third trilogy - the story of the fall and redemption of Anakin Skywalker is over.
There are several directions a third trilogy could take. The best might be to do a "Dallas", with Luke waking up back on the farm and telling his uncle, "I had the strangest dream last night." The uncle would then tell him, "Your father is here for a visit." Darth Vader would then walk in.