Can your terminal do emojis? How big?

In my fever dreams of maintaining utf8 supporting text widgets that work and never need to be updated, there's a zero-width whitespace grapheme cluster that represents the number of codepoints in the next grapheme cluster if they're different from the previous.

The situation today is basically the same as null terminated C strings. Except worse, because you can define that problem and solve it in linear time/space without needing to keep an up to date list of tables.

This has nothing to do with UTF-8 which doesn't and shouldn't care about anything beyond mapping bytes to code points.

But even for adding it to Unicode, your proposal would make text stateful (even over long distances) which is a really bad idea.