Why's all the pressure on me? This is a community project (no, really!), so anyone can have a go at upgrading the Editor.
I assume we're talking about the External Editor here. I think there's only about two things it does that can't be done in-game anyway: the animation editor and repositioning sprites. Frankly, I don't really see how it's difficult to edit the PBS files directly, since half the time there are hundreds of examples (moves, Pokémon, etc.).
The day/night system is touchy at best, and seems to show the correct tint only when it feels like it (although I don't know why). I'm sure it would be pretty difficult to allow a "preview" of a tint. The tints themselves are in the array HourlyTones at the top of PokemonTime, and are not something people would usually want to change which is why they're not in Settings.
If you have any more suggestions for Settings, please let me know.