I wouldn’t be surprised if new scenes (with Margot and Feyd) are being made for Part 1 as well, with a Godfather Saga-esque extended edition in the not-too-distant future.
I think Villeneuve stated that he doesn't plan on doing a Director's Cut or something like it and regards his Dune movie as the definitive cut ( they filmed material though for many more hours which didn't make it into the movie). I'm fine with it, the first movie is great as it is and i'd rather not he Lucas it and change things every few years.
Once can never know though, the studio might get greedy and start messing around but if there are no scenes filmed to be retroactively included then we're safe.