Newer Yubikeys (since firmware 5.2.3) support ed25519, cv25519 and brainpool curves. we need to test them and make them work flawlessly. It might also be useful to use them by default for the OpenPGP app.
I am interested in that. I have a yubikey here that I wish to use productively for brainpool-256 signing, bp-512 (just for fun) encrypting and cv25519 authentication. I need to use brainpool signing and encryption subkeys for VS-NfD compliant communication and I want to be more modern then RSA ;-)
@gniibe: If you need a yubikey with that firmware I can give you one when you are in europe next week or at Fosdem.