I actually flashed lineage onto an old (5th gen?) Amazon Fire tablet I had gathering dust recently. I've been very satisfied with the result, but I'm personally not at the point where I'd trust it as my daily driver OS. My smartphone holds sensitive bank data, I rely on it to call for help in emergencies, I use it as an alarm clock to ensure I get to work on time, etc. There's just too much at stake for me to trust pulling a build off some thread on XDA-developers and hoping for the best.

quick edit: Maybe there's collaborative a way forward though, where the LineageOS community and Fairphone work together to extend support through Fairphone approved Lineage releases. I'd totally be down for that.