How about Haydens face? NOPE!
Sebastians face? No, as Luke has never met him.
OBWans face? Possibilty, and open for debate.
Then it came to me!
To make scence of the scene, from the trilogy point of view when it was made, Darth Vaders mask should have had LEIA's face inside it!
-It would tell me Lukes training is being destracted by thoughts of his friends, at an early stage, hence Yodas later statement.
-Make Luke feel like he is on the path to the darkside, by destroying people who he loves by being the aggressor in combat.
-And ultimately, he would be able to destroy the only other Skywalker (the final hope) if he maintained his current way of thinking - that making the difference as to why he didnt need anymore training in Jedi, as he had felt it.
It would make total scence of the scene, to me, and give one of those wow, thats been changed for better moments, that i loved many times, during watching ANHrevisited.....
Or, if i want to be silly R2-D2s head, as he'd stuck by Luke through thick and thin, and also serverd his daddy in the clone wars!