Janus/Criterion screened both TROG and Biollante at Alamo Drafthouse cinemas in 2021 as the Janus logo did appear before the very beginning of those films, so it’s likely that they have been in talks with Toho about acquiring the rest of the films. As for Sony, GvKG and GvM’s rights were up for renewal in 2019 and it appears that most of the rights for those films have expired now. As stated before, the rest of the Heisei era, GxM, GMK and the first two Rebirth of Mothra films were up for renewal in 2023 while the rest seem to be renewable in 2025.
A future Heisei and Millennium collection seems likely at this point. Given that the set would probably come out around 2025 Toho have enough time to release their TROG 4K remaster onto disc, which hopefully means that both 4K remasters for TROG and Biollante will be given to Criterion, but if Toho have not made any 4K versions for the rest of the films by that time and then released them on disc in Japan then it’s likely we’ll get the Hi-Vision masters for the rest of the films with some touch ups. It’s possible that we get more supplements this time around as the Heisei set would only have 7 films while a Millennium set would only have 6, unless Criterion merge the Heisei and Millennium series together in the same set.
I just hope we get all English dubs this time around, I hated how some of the films on the Showa set didn’t get their dubs, especially since the Criterion set is the only legal way to watch these films in the UK right now. Would really like to hear what that unreleased G2K Omni dub sounds like, hell I’d even like to get the “pre-repairs” dub of GvMGII. I hope they could potentially get the rights to G85 but that’s a whole legal mess, they’d probably get a higher chance of getting the US cuts of the Showa films, but then again the last time we heard about legal issues with G85 were around the Kraken release and a lot can change in just a few years.