This strategy was used by the Cwicly team for v1.3 to introduce the Components features.
The biggest issue at that time was ensuring synchronisation between the release channel and the beta channel, otherwise it is harder to switch between them to test out features.
I think a beta channel can work well as long as the iterations are on the shorter side and/or any bug fixes and enhancements from the release channel are kept in sync.
This is an interesting one. I have seen many very good plugins switch to modularisation using multiple separate add-ons and then switch back to a single “Pro” plugin for various reasons.
In theory having separate modular add-ons can be good to keep the file size lower and only include what is needed. On the other hand, it does require additional maintenance, keeping everything in sync and can lead to some duplication for each plugin.
On hosts like SiteGround which has “Inode” restrictions, the number of files can also be more of a significant factor than the size of the files.
I think a reasonable compromise initially may be to make each release go through a short beta stage. This would increase the time to get each release out but would likely catch many bugs / conflicts before they can affect a lot of users.