I would definitely be onboard for a mild refresh. I would hope for something that would (a) support backwards compatibility, much as you say here, but also (b) address some balance/flavor issues that both the players and designers seem to have with the various character options and possibly some of the ambiguous ruling areas (e.g., stealth, vision, and lighting). I could also foresee that a new edition would swap out less popular core character options for more popular options from later books. (Could the half-orc just be replaced with the orc? Possibly.)
I would definitely be curious whether the designers would use the opportunity to scratch some of their personal design irks. Mearls, for example, wished in hindsight that the warlock was designed differently regarding the interaction between their patron/boon. So I would be curious whether or not things like that would change if they had the opportunity to refresh or whether they would keep it the same.
Edit: I am curious what people see within the acceptable boundaries of a "refresh" and which things should remain untouched, though that may just repeat a lot of the same points raised in this thread.
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