I believe you're describing F-Droid.

That solves the "app store" problem, the OS is still hostile though, and even using Replicant the Baseband OS is still a threat.

Not using F-Droid wouldn't be better, it is just that it really seams hopeless for a complete solution without a major movement like what spawned GNU-Linux. All these problems need way more devs involved.

Why is the OS still hostile when using an AOSP based ROM?

From what I understand it isn't possible to run AOSP on the vast majority of hardware. You still need proprietary binary blobs for the drivers and the baseband OS.

You don't need it to run on the majority of hardware. Just need one device that runs AOSP and meets whatever other requirements you may have.

I agree, but it's a pain. I tried to run AOSP on an Xperia XA2. You are missing so much. Sony doesn't offer much software for your hardware on AOSP. F-Droid has like three orders of magnitude less apps than the play store. Even the many apps that don't rely on google features, hell even competitors like Microsoft offer e.g. their Word for Android nowhere else. In the end, you probably will install google services non the less, but this time from less trustworthy sources since google doesn't officially want or will help you getting their stuff run on ASOP.

The system was generally unstable. I finally gave up when I noticed video playback in landscape mode turns the screen green, but works fine in vertical (Different apps, even ASOP stock apps, even after fresh re-compile)

I'm now going the other route... using a sony image and rip out everything unnecessary. Neither seems worth the time for average consumers. Learned a lot, though.

I honestly don’t think that would ever happen, for many reasons, the first being funding, and the second being network effects.

Don't forget reproducible builds as one of the major open source features :)

I'm waiting for the Purism Librem 5. Should be interesting.