I know the idea of Open-Sourcing Sublime Text has been discussed here before and (mostly) rejected, but I wonder if something like the Time-limited Business Source License (BSL) that CockRoachDB uses might work for Sublime HQ’s pricing model - where the code reverts to an open source license X years after release but is proprietary before that, allowing you to continue charging for updates etc.
That way at least older versions could be open sourced and the community could be sure that the source code will always be available if Sublime HQ themselves ever stopped development of it.