Interested in this topic as well.
We are not implementing multi-tenancy but we did have a lot of issues with doing APM and multiple route-domains. For example Java-based-RDP started supporting route-domains only with 11.6.0+HF4.
Also for our SSLVPN access, we have a separate route-domain (e.g. %1), but I observe that certain traffic does not work well with that. For e.g. when a DHCP broadcast happens on the SSL-VPN subnet, we wanted to setup a DHCP relay VS and relay the DHCP requests out our DHCP servers (like cisco ip-helper) but never got it to work.
cheers.