> But the thing is that in 20-30 years we won't be able to invent any new writing systems that UTF-8 won't cover.

I think you underestimate humanity's aptitude at creating things that don't fit into well defined standards.

My (admittedly poorly stated) point wasn't that we shouldn't be moving everything over to UTF-8. I personally use it wherever possible just because it makes life easier. My point was that there are decades of things that use ASCII-US or another one of the overlapping but incompatible encodings because they were the RightThing™ to use at the time and there's no way we're going to get rid of everything non-UTF-8 any time soon.

In 20-30 years we'll be saying "Why isn't everything in FutureText-64, it should be the only encoding. Why does anything else even exist?", and it'll be because we're saying the same about UTF-8 now.