F-Droid says Google’s new sideloading restrictions will kill the project

Correct. But we don’t know yet whether this will make it into AOSP (if it still exists by then) in QPR2, or it will be only for OEMs.

In any case, if it makes into AOSP a dev can just remove it. The concern I have is if it goes into AOSP even Chinese-market phones will be impacted (not that I use one).