That would be perfect for various servers (simple web or DNS server, full-featured OpenVPN server. As a limited user, in isolated environment, to not influence the base system too much.
What could work, would be a new RouterOS feature that would allow user to run custom binaries. But I don't think there's a market for any special RB device connectable to RPi.
People are asking MikroTik for Oh yeah, me, here.
