Appeal is the sort of thing that could be a bedrock mechanic that other systems are based off of, to help tie everything together. It's a universal measure of how "nice" it is to live in a particular area. Even the game graphics could perhaps show this in some form or another.
Within the context of Civ 6's existing framework, perhaps the easiest change that would (I think) generally improve gameplay would be to tie Appeal directly to Amenities (which themselves then tie to Loyalty, Productivity, etc. through the Happiness system). Something like:
- Working a tile or having a District on a tile with Charming Appeal or better gives +1 Amenity
- Working a tile or having a District on a tile with Uninviting Appeal gives -1 Amenity
- Working a tile or having a District on a tile with Disgusting Appeal gives -2 Amenities
This nerfs mines, which are the primarily source of production currently, so that knock on effect would have to be considered and addressed. That would be good, though, to my mind, as mining every hill in the game and having people work those hills instead of working in a Factory is a bit immersion breaking to me.