UTF-8 can represent up to 1,114,112 characters in Unicode. And in Unicode 15.1 (2023, https://www.unicode.org/versions/Unicode15.1.0/) a total of 149,813 characters are included, which covers most of the world's languages, scripts, and emojis. That leaves a 960K space for future expansion.

So, it won't fill up during our lifetime I guess.

I wouldn't be too quick to jump to that conclusion, we could easily shove another 960k emojis into the spec!

Wait until we get to know another specie then we will not just fill that Unicode space, but we will ditch any utf-16 compatibility so fast that will make your head spin on a snivel.

Imagine the code points we'll need to represent an alien culture :).