I do not agree that Unicode is good. I think that Unicode is not good.

I also think that, regardless of the character set, what to include (control characters, graphic characters, maximum length, etc) will have to depend on the specific application anyways, so trying to include/exclude in JSON doesn't work as well.

Giving a name to a specific subset (or sometimes a superset, but usually subset) of Unicode (or any other character sets, such as ASCII or ISO 2022 or TRON code) can be useful, but don't assume it is good for everyone or even is good for most things, because it isn't.

RFC 9839 does give names to some subsets of Unicode, which may sometimes be useful, but should not automatically assume that is right for what you will be making. My opinion is to consider to not use or require Unicode.

It's really the combining characters that are the problem. That changed it from a character set to a DSL for describing characters.