If Darth Vader really wanted to kill Luke, he'd have torn him apart. The Emperor wanted Luke to kill Vader, because Luke had the potential (emphasis on potential) to become stronger than Vader, and killing him would help turn him to the dark side. Luke, at the time, was not stronger than Vader. Also, currently (in the New Jedi Order series), Luke, while very powerful, is still not as powerful as the emperor was. I say this, because he'd have to be a bit older to become as powerful as the emperor. Remember, the jedi he trained could become more powerul than him easily (well, not so easily, but they could). However, there are still no jedi who are stronger than he. Kyle actually did have training, Rahn as a spirit trained him, although he had no physical lightsaber training. So, Luke would win.
Also, before someone brings this up on the forum, which I know they will eventually, Qui-Gon was right about Anakin being the chosen one. Think about it, if Anakin hadn't turned to the dark side, he'd have been hunted down with all the other Jedi by the emperor who was the most powerful force user at the time (other than Yoda & Co.). Turning to the dark side allowed him to survive long enough to kill the emperor. While I admitt that without Luke to prompt his return to the lightside, he would not have done it, Luke was not powerful enough himself to kill the emperor. Without Darth Vader, Luke would be dead. So, in the end, Qui-Gon was right, and Anakin was the chosen one.
"Shut up Arcturus, if I wanted your damn opinion I would have beaten it out of ya." - Former Marshal James Raynor