> Stuff like LineageOS is kind of a start, but they're constantly fighting to get a toehold on each new smartphone generation.

That's because the SoC's themselves have almost zero standardization - and quite unlike the custom platforms of the 1980s and 1990s, they aren't even documented. They can barely run with their hacked-together 'board support packages (BSP's)' and factory-installed OS's. Cleaning up the hardware support for even a single one of these platforms so it passes the standards for mainline kernel inclusion and support is a huge amount of effort, and then only gives you long-term support for that one hardware revision. It's a lot worse of a mess than what we had in the 1990s.

Exactly, and it seems so unnecessary. These problems were solved on PCs in the 90s and the cell phone manufacturers are absolutely refusing to use the solutions. I can only imagine how many man-years of effort have been wasted because they're so insistent on keeping everything siloed up. It is madness.

We are are already living in that world, the shrinking "build your desktop" market is the surviving species of PC clones.

Everyone that moved into laptops as their main computer are split between Windows/macOS laptops, with a negligible market size for anything else.

Are people hacking smartphones like those closed source microcomputers were hacked as described in Hackers: Heroes of Computer Revolution" by Steven Levy?