It's possible to do it without their connect API for sure, but that would require users to
1. Look up their ssh password
2. Connect tablet to their computer
3. Run a (my) program on their computer to install custom sync software on the tablet
I'm not focusing on the technically capable ReMarkable users so I opted not to do this. Besides, it would involve a lot more development time which I don't have a lot of as I have a day-job as well.