Han unification isn't main blocker to transition to utf-8 in Japan. Just use Japanese font in this context.
Why SJIS is still used is because there are many legacy systems and developers who still think SJIS is fine. We not tend to treat other languages so it mostly works (without emoji).
SJIS is sometimes useful because 1-byte char is half width, and 2-bytes char is full width by design. Old developers still call Japanese character as "2-bytes character" even though the system is utf-8.
Why SJIS is still used is because there are many legacy systems and developers who still think SJIS is fine. We not tend to treat other languages so it mostly works (without emoji). SJIS is sometimes useful because 1-byte char is half width, and 2-bytes char is full width by design. Old developers still call Japanese character as "2-bytes character" even though the system is utf-8.
Another reason is that Windows OEM codepage is still CP932 (extended SJIS). It's pain like this: https://discuss.python.org/t/pep-597-enable-utf-8-mode-by-de...