Problem: MediaWiki's support for security keys (for example YubiKeys) via WebAuthn for two-factor authentication is, well, not very good. There are two main issues:
Security keys are tied to a single wiki. Combined with the broken cross-wiki auto-login mechanism this makes it annoying to log in.
It is only possible to add a single key to an account. Best practices for using security keys include having several keys with access in case a single key is damaged or lost.
Proposed solution: Fix the bugs mentioned above.
Who would benefit: Users who want to secure their user accounts.