Ok, I've had this running for years now, so this is mostly a 'do not forget' note-to-self. Rancid supports backing up MikroTik RouterOS configuration.
Add a readonly user to your RouterOS device:
/user add group=read name=rancid disabled=no password=huwakui5phiiVahnuecheiri
# use a long random password
Add the user/password to your .cloginrc:
add user 10.0.0.1 rancid
add noenable 10.0.0.1 1
add password 10.0.0.1 huwakui5phiiVahnuecheiri
add method 10.0.0.1 ssh
... and add the router to router.db:
10.0.0.1;mikrotik;up