I'd wager they will require deb packages to be signed with a certain Canonical key that they will use strictly for basic system packages. Everything else will be a sandboxed Snap, left to third-parties to maintain, distributed through a Canonical Appstore that enables payments.
Maybe they will give you an option to "root" the system, and if you use it you'll lose any right to support or updates from Canonical.
Snap is fundamentally a commercial play to reduce support costs and enable an appstore.
IF they do that I'm obviously leaving their ecosystem, though I'm just a consumer so no clue how much effect I would have.
I really don't see what benefit that would provide them over other distros though and I'm not sure why they would make that choice to close down their system?
Fundamentally Linux works so well because of the free software movement and I don't see any app maintainers choosing to charge a fee for their software if they aren't already.
Arguably the Linux desktop ecosystem does not “work so well”. Adoption rates are still minuscule when compared to Apple or Microsoft numbers, and there is precious little support from commercial developers. The “year of Linux on the desktop” never happened, even after Canonical made it really simple to run Linux, so commercial support is still lacking - which in turn keeps users away. The Snap play is their latest attempt to increase monetization rates on the platform.
Slowly boiling the frog is really effective.