The idea that a Vader style suit is worn by many jedi is intriguing to me. Vader's 'sad devotion to that ancient religion' and his status as 'the last of their kind' could be quite literal in that he is the only one still wearing the jedi costume. Also provides some cover for the idea that "Vader" killed Anakin, since Vader could have been any bad jedi.

I'm not sold on there being another Darth Vader. I think I'd need to see how it works within a story.

Here are my ideas which I've expressed to some extent in this forum (the following is mostly copypasted from another forum, where I recognize at least one member from here):

Let Anakin go off to the volcano planet to meet Palpatine, leaving his saber behind with Obi Wan to give to his still unborn child. It will be reminiscent of Luke going into the cave on Dagobah, except Anakin leaves his weapon of his own motivation. For the audience it may be ambiguous whether Anakin is joining the dark side or nobly sacrificing himself. We show Anakin confront Palpatine. Then the scene cuts to Obi Wan who, after some hesitation, goes to save his friend. I am leaning toward not showing a duel between Obi Wan and Anakin.

Later on Vader duels Obi Wan. Obi Wan double talks about Vader killing Anakin. In this way, Obi Wan's later explanation to Luke is seen as less of a jerky plot gimmick and more of 'this is seriously how Obi Wan sees the world.' Vader retorts that it was Obi Wan who killed Anakin (double meaning of 'drove him to the dark side' and 'literally sliced him up').

If many jedi wear Vader style clothing, it can be even more believable that Vader is someone other than Anakin.

As for this epic duel, here is something I wonder:

I think we all have it burned into our minds that Anakin gets the Vader suit following a duel with Obi Wan. Even those of us who have little regard for the EU. I can't remember if it's from the novelization? But I guess that is how it should be. What do you think?