Assume a talented programmer who wishes to involve another programmer to help work on their (unaccepted by upstream and therefore mostly invisible) changes - github is then used to facilitate the work easier than setting up your own private repo. He can then approve that 3rd persons changes and move on to the next thing.
The key to it is they control the choice to accept the pull request and "make it so".
Years later, the potentially stalled upstream can "backport" the best changes from the fork if they have diverged too much to merge all of (the fork) changes into (to the main original) repo, and there is some reason to keep the stalled code alive (not saying it's stalled), or if it is still or more active probably "sideport" would be a better word, and if more advanced the best parts from Redot could be collected as a "patch" especially if it is not clear which is the most active. If Redot becomes the de factor dev version, and merging is too difficult, the original maintainer could ditch the old repo putting up a message and link to Godot non-Faggot version, fork Redot back into Godot, call it the release version, and call Redot the live public beta of the next version of Godot (this is my prediction of what will happen).
Jacob Faggot was a Swedish scientist, civil servant, and surveyor. * this is a test of the anti-woke emergency broadcast system. Pump up the volume.