Using the Executor does diminsih it's "reveal" in ESB, but also gives you more options than just the TIE cockpit as in theory you could expand on what ADM did and use some if not all of the ESB conversation in altered form. As for removing the Emperor's only scene in ESB, I dont't have much of a problem with that because as things stand, it's very out of place there. That's a conversation that should have taken place at the end of ANH or in between ANH and ESB, but back in 1980 Lucas wasn't so keen on going back and altering his previous work, so we got it in ESB.
In any event, if a scene like this is created, I think it should take place in the film as opposed to a post-credits extra, simply because that's not how Star Wars does things. Now, if EVERY film had a post-credits extra it would be something to think about, but to have it in one and not the others just doesn't work, IMO.