Fan editors often use several sources, some not easily available (a good example might be Lynch’s Dune where there’s a heavily cut theatrical version, an extended TV version and deleted scenes). The sources might have different quality, and some need adjustments/filters to fit back in with the rest. Then, the audio needs to be fixed over the cuts. Otherwise, you’d get, e.g., the music skipping around. Etc. Etc.
All that said, it’s a very cool idea … but even if technically possible, it would restrict the art of re-cutting quite a bit compared to what they are doing now 
