Have you looked at the BOOX tablets?
I have an Note air 2, which is very similar to remarkable. The software is just android with a different UI. You can install whatever android app you want, transfer any file you want and so on.
It is about as non locked down as you can get for a "normal" tablet, which you can't say about the amazon devices...
Yes, i have actually narrowed it down to some sort of BOOX prior to the Scribe being released.
Will delay my purchase for a bit and do another review of the BOOX offering vs Scribe.
Amazon's devices are locked down (their tablets are terrible for this) but the kindle is a simple device and easy to side-load books bought elsewhere so it works well for me.
It is about as non locked down as you can get for a "normal" tablet, which you can't say about the amazon devices...