I would love something like the Remarkable tablet. However I'm not buying a niche hardware product to have my data held hostage by monthly cloud sync fees. Let me use Nextcloud or a service I've already paid for.
The cloud is optional and you have a root SSH access to the tablet. It's possible to impl. your own service for syncing or just sync via SSH with scripts.
You can self-host rmfakecloud, an open-source reimplementation of the reMarkable cloud. You just ssh into the device and use a DNS trick to swap it out.