I have been asked in PM whether it would be eventually possible, using a more powerful computer, to simply re-render the Premiere project for the edit in 1080p.

Putting aside the fact that I had other reasons to go with 720p (although admittedly, computing power was the main one) this is not possible anyway, since the last work I did in Premiere was on v2.0 - I've been using the lossless master for v2.0 in After Effects to create v2.1 and v2.5 and I wasn't even working with the BD in Premiere for v2.0 but rather with a 720p lossless encode of a preliminarily Avisynth color-correction by You_Too, which I don't have any more and which would be pretty much impossible to re-create, since it was split rather randomly into several parts. Plus all the despecialized shots were done and rendered individually in After Effects, often with many intermediate steps and pre-renders. And all this was done with very little organization (a mistake I'm trying to avoid on ESB and ROTJ v2.0s) so it would probably be easier to redo the edit from scratch, than to try re-rendering everything using the project files.