I also interested in slugs with transliteration.
But, I think, It could be done from the plugin, main idea is to use hooks around create methods.
Areas where It could be used:Topic titles Categories User names
I have 2 plugins in plans: utils - to reconstruct in-place slugs, for me It's easier to have lightweight utility, than very heavy import script; slugs - I'm also not happy with Cyrillic letters in urls
@julian slugs are really good candidate for core improvement