As someone who's battled with fixing the prequels in my own edits, I can see where the cynicism comes from. They are improveable (mainly by making them shorter and cutting lots of the crap) but they are not fixable just by trimming a scene here, changing the order there, etc.

But we already know that Adywan's versions are not going to be straightforward re-edits. We have no idea how ambitious his Prequels will be, but from the snippets we've actually been told, it's going to be a complete deconstruction and then reconstruction to make a coherent story where there wasn't one before.

There is bound to be redubbing. I simply can't see any other way around the shitty dialogue and character motivations in the prequels. It's unsalvageable. At least a couple of characters need to be given new lines in cutaways so redubbing with new voice acting talent would be the only way to go.

We already know he's filming new footage with existing characters. (Threepio and maybe others, who knows?)

He has heavily hinted that a certain Grand Moff will appear, so he's adding new actors too, possibly with dialogue.

It's safe to assume there will be substantial miniature work. Maybe even new motion-control or CG space battles.

The point is, I don't know how anyone can make an assertion about it being impossible after knowing all that. We have no idea how much of the original films will even be left when he's done!