Aside from the multiple plot issues as previously mentioned which would have to be addressed I would hesitate to cut out so much of the big conclusion of ep.3.

"I know the whole burning and chopping thing looks pretty cool and it allows using the whole Vader transformation scene (which is also cool), but we could live without it and just imagine that Vader became robotic somehow in the time between EPIII and EPIV."

Personally I'd hate to edit out Anakin becoming Vader. For me at least - that's such an awesome and iconic moment in the saga. I dig almost every bit of that from the moment Anakin is violently cut down to his ultimate grisly transformation.

Those are my favorite moments of ROTS.