Too much concern about the reveal, as if it were the pivotal point of the whole saga.
Think how the prequels played out, and you'll find that if Vader spoke his truth it would have been a truthful and strong moment as in I am your father.
They could have kept the original ObiWan killed your father, and it would still be true and an "awesome WTF moment"
This meaning there might not be a point in making the effort to twist 600 minutes of PT just to preserve 1 minute of OT no matter how idolised by the pop culture that moment is.
Even if you somehow managed to make Maul survive and be Grievous, and Grievous "be" Vader, or make Dooku be Vader, or if you filmed a second apprentice to ObiWan just to make him be Vader, you would still have Anakin going down and falling, regardless of whether you cut mustafar out or not.
What's more that could be pleasing to watch as a fan edit, where you constantly are subject to the tought of "he moved the pieces that way, and took this off and put this, etc." but if you saw that movie for the first time, it might feel rather inconclussive. This is what I think is the real trouble of "fixing" the PT to match the OT when it comes to Anakin's "secret": best case scenario is a film where you have this iconical war hero, who is the protagonist of the movie and at some points dissappears but he doesn't have a funeral, nor a mention. Inconclussive. And if you add to that the fact that a black knight with heroic proportions now replaces the old cyborg that would-have-used to be the sidekick of the emperor, there's little room for secrecy.
I think it might be too much effort wasted. Darth Vader can very well be a pathetic character without diminishing him. It's us who believed he suddenly was the primal source of evil and power. And, in a big exercise of fan-service Lucas made Anakin be "the chosen one" and all sorts of things that enhightened his position within the hierarchy of the Jedi and thus the Sith.
OT is different and always was. It was sillier. There are humorous scenes with Vader in ESB, it's us who want him to be more "badass" than he is. And that has made the Star Wars experience flatter. Perhaps the problem is to believe that everything should have been darker and more serious while maybe the real thing is to make it more innocent, naive.
Have you seen how stupid does Kylo Ren look in the trailer of TFA when he makes a completely ridicolous stance just to activate his sabre? That's because Abrahams is a fanboy too. I want vilains to be bad people, not cartoons of evil.