I think a better way to put "multiple ways to implement" is "different possible solutions". For file watchers, if MG provides such a thing, there's really no reason for people to implement their own version of it. You get notified when assets change, there's maybe different ways to implement it, but that's the functionality you want. If you want some extended features you can build on top of that. That's completely different from e.g. a Tiled implementation, because there's lots of possibilities for the API and what exactly is supported. If MG implements that one way, some people might not like it and implement their own. IMO that means it's out of the scope of MG.
I also think that list of requirements should be looked at case-by-case and not used as a hard measure. For example you mentioned font processing/displaying in the GitHub issue: there's a ton of different ways to render glyphs, but it's essential to most games, so it makes sense for MG to implement it some way.