How important are reddit-style flairs for people? There's the raised issue https://github.com/LemmyNet/lemmy/issues/317 which has it listed as a far-future, with questions as far as how to handle federation.
Personally, having at least an initial implementation done on a community level would be largely sufficient, with expansion to instance-wide being optional. The situation I've found most useful, personally, is sports-related groups with your favored team being your flair. This gives context to comments without constantly having to say "as a X fan"
We used flairs on the Lockpicking sub as awards as people progressed through different levels of locksport. I'm dreading having to give thousands of those out again here if user flairs are a thing.