I imagine that they're wildly less effective at reverse engineering firmware for random chips than software for common platforms

> I don't understand why they wouldn't try to further liberate the phone that already runs an FSF-endorsed operating system, Librem 5. Perhaps one argument is to support more phones - but instead they could demonstrate a proof of concept for the most free phone, which is what I would expect from the FSF.

A cynical take would be that they're trying to sabotage the concept so it's unusable for non-techies.

A slightly more realistic take is that having their own phone is better PR than supporting someone else's, even if it is just a custom Android ROM instead of an actual Linux distro.

> Also, AOSP obeys Google's development strategy, so even though it's free software, it is not a good bet long term.

Check https://librephone.fsf.org :

«This is not another Android distribution, but a long-term effort to understand and reverse-engineer the nonfree components used in nearly all SoCs today»