OpenSSH has the TrustedUserCAKeys option, which enables one to allow access to all users that have a signed public key by the specified CA (certificate authority). So there’s no need to configure each users ssh keys on the routes.
I feel just as guilty as @KisukeCZE for necro-bumping, but I would like to insist: when managing devices at scale, it would be really useful to have that SSH feature. I believe it’s been implemented more than a decade ago in OpenSSH, Juniper is now supporting it, Arista has it too, maybe it’s time for Mikrotik to give it a go?