I know you're not considering it for now, but I'd surely like to have such device with SFOS, even if it's unofficial port. Parts of libhybris-based adaptation could then be reused for another Linux-based OS. Also, there is a thread about porting Freemantle UI to GTK 3. Could MTK chips be used to lower up the cost? Something about GPD Win price seems reasonable to me.
What about graphics systems ? GPU support ? If wayland based Tizen/E can be supported too. What about Nemomobile too ?