
Canonical is going to make the current Snapcraft codebase "legacy" while they are working their latest code into a new, more modular architecture. At the moment it's at a stage of "the early proof of concept only covers some aspects of the Snapcraft functionality, but it did illustrate a relatively quick conversion to the new modular design."
A lot of new code is to be written for improving the Snapcraft architecture but that seems to be what is on their agenda for 2022. While a radical change, they don't expect it to interrupt the current Snapcraft usage model and projects relying on core18/core20 states will continue to be able to leverage the monolithic "legacy" Snapcraft and when ready can transition to the new codebase.
The light blog post today concludes with, " To boldly go where no one has gone before. This is true for spacecraft as well as Snapcraft. Going forward, you should expect to see quite a few new, interesting developments in the product, all aimed at making things simpler, faster, more robust, and without adversely affecting the user experience. "