You are probably right: the biggest problem for Jolla would be to get out of this tiny niche. IMHO the OS is almost ready for a broad market. So what is lacking is partners that sell devices with Sailfish OS.

I regard the Jolla Phone a demonstrator. Jolla can't do it all (software and devices) alone - even Blackberry could not, although they at least had pretty deep pockets.

Sailfish OS could become fashionable. It needs some luck, though.