I agree, mostly what I meant too. Device drivers is the big problem. But the fact is that 100% of Jolla devices so far run Android kernel and libhybris. Even the tablet that is Intel x86 hardware (I have a Jolla tablet, too)!
Once drivers are overcome, any FLOSS distro could run on the device.
For sure GUI applications need some tweaking for phone use and touch interface. Sailfish is also partly closed source at GUI level.