Bit late reMarkable is running Linux and the community is providing tools like https://github.com/ddvk/rmfakecloud

That's a pretty cool project. But with it living in the grey area of not being really supported by Remarkable, I would be skeptical if Remarkable does not block it down the line.

Supernote has full-fledged Linux support in the official pipeline. It has gotten postponed quite recently, so the devices still run on their customized Android distribution only. But even in the current state, I feel more ownership over my HW and SW than I would with Remarkable.

It's been about 6 years so I doubt it.

If they do though then I won't update and won't buy the next model. I can imagine them doing it for a new model for already sold one that'd be a first.

FWIW if you really want ownership and don't care much for weight the PineNote is probably the best our there, able to run Android (with root) but also Linux proper.