Why does everyone asume that it is absolutely key to keep Vader’s identity a secret? Doing it will not take us 30 years back in history, and will not make us stand in awe as we did when we were kids watching the movie. There’s no point in insisting that Bespin is “the” defining moment of the saga. Infact, it all started with ANH, which did very well without any reveal at all.
Honestly, not only I do not think there is a way to pull it out, but I suspect there can’t be a strong reason to make that titanic effort as well. Of course it is a point given by Adywan that he will adress this. Furthermore he even gave us hints at how would he adress this, so I’m not questioning his decissions, but more of writing this in this thread which in a lot of ways behaves as a pool of collective thinking for more than just Ady’s edit.
Even if you manage to avoid any reference or scene featuring Anakin’s falli to the dark side in the PT, there’s still that line in ANH from Vader to Tarkin: “my old master is here” which is most problematic to the proposed scheme.
In any case, even if the PT was tweaked to have ObiWan have two apprentices, that would only reduce the chance of Vader being Anakin to a 50%.
If you show Anakin’s death in ROTS by ObiWan’s hands, then that would make a liar of ObiWan and make the whole tale he gives Luke be suspicious anyway (let alone the fact that cutting mustafar out of the movie would significantly create plot holes and drastically reduce the runtime).
If you don’t show Anakin’s death at all, then by ANH there’s the obvious question where is Anakin and why does ObiWan reference something we didn’t see.
And all of these are “grand scheme” problems. If instead we started to analyse the issues in a smaller scale there would be problems within the structure of each movie (who kills Windu, why does Padmè go to Mustafar, what happened to all the battledroids, etc)
If the saga as a whole is a project, then forcing more (considering some parts of ANH would be problematic as well) than three movies to fit one moment is as wrong as it would be to force the distribution of a house around the desire of its owner to have a certain kind of lamp. IMO it might be better to move on from that and try to make the saga a better and more complex work.
Short of having new material or being willing to edit both the PT and the OT, you can’t make Vader a plot twist. Instead, however, you can make Bespin be a very tragic moment with the material available, and always watch the saga 4|5|6|1|2|3 if you wanted to preserve the “reveal”.