Sadly, most of the more recent additions have either no copyright header or an explicit “License: Proprietary” notice. It seems these files were mostly modified by Open Mobile Platform and now that Jolla is severing ties with Russia, maybe they (Jolla) can rethink their stance…
That should be possible but its a massive and unnecessary amount of work - Jolla could simply decide to open it up. All the things people are patching now through Patchmanager could then be upstreamed.
Exactly, plus it would make Sailfish independent of Jolla’s financial situation. If they decide one day to discontinue Sailfish, or if they don’t have the money to continue, then all the community effort has been for nothing as all Sailfish apps can’t run anywhere else.

