Although customer support is limited as stated behind: https://confluence.atlassian.com/bitbucketserverkb/viewing-or-updating-the-bitbucket-server-ssh-private-key-824344744.html

I like to request support for elliptic server keys. like ECDSA or ED25519.

I tried with an ECDSA Key but on connection test I got:

[sshd-SshServer[24cd1d40]-nio2-thread-1]  c.a.b.i.s.s.DefaultHostKeyPairProvider resolveKeyPair(/var/atlassian/application-data/bitbucket/shared/config/ssh-server-keys.pem) mismatched loaded key algorithm: expected=RSA, loaded=EC 

So I assume the implemented mina-sshd only accepts RSA. Would be nice you could extend it

This might give a little speedup in kex.

Thank you