I'm not entirely sure if that would be better than just adopting PostmarketOS, since forking AOSP would mean maintaining a fork of that entire ecosystem, and I'm unsure how they would deal with all the phone manufacturers dropping support for phones rather quickly, or using outdated kernels to access GPU and hardware drivers for said phones after the manufacturer drops support. Investing in PostmarketOS instead would bring with it much less stuff to fork, along with access to the mainline linux kernel (instead of outdated Android ones) that use open-source GPU drivers that can be effectively maintained, and it can support Android compatibility with a compatibility layer, Waydroid. A polished PostmarketOS ecosystem only seems to offer advantages compared to a forked AOSP, so if they're choosing which to invest in, Postmarket seems like the clear winner.