The Steam Deck sort of occupies this space today. I'm not in the scene myself but I've read about users modding them, running unsupported OSs, liquid cooling them, etc. Seems like any sufficiently broad technology will garner a community of hackers and modders around it.
I'm not into modding but I got SD because of it's openness and all sorts of things I can make with it (also to support gaming on Linux and kudos do Valve for the work on pushing it ;) )
I played with jolla/sailfish for a while and the device was awesome but I couldn't get myself to like gesture/swipe navigation (I hate it on the current flock of iOS/Android with same passion)...
For the device I'm pondering new OP which is more open than the rest but still, as you said - it's mostly the same OS and the changes are not that significant to spend all that time on flashing...
