Han unification is one problem; another problem is that not all encodings can be round-tripped losslessly through Unicode. Shift-JIS, for example, has multiple separate characters that convert into the same character in Unicode, and therefore cannot be converted back into their original form reliably.

Wow. That's pretty ugly, thanks for the info. But for people not wanting to use Unicode... Does that not mean they simply cannot use strings in Java, .Net, Windows (to some extent), etc.? It just seems sorta not feasible at this point to not use Unicode. And according to Wikipedia, Unicode now has a way to select which language variant of a unified character. So is unification not as big a problem if people use selectors?

And what's the practical alternative? Keeping things in country specific encodings?