I'd like it if the router had an additional IP associated with it, which could be used in port forwarding and serve a customisable page. So if we took our usual webserver down for planned maintenance, any incoming port 80 traffic could be forwarded instead to this other page that would say "server down come back in (whatever) instead of just an anonymous error. Currently I have to keep a NAS server on standby just for this, but it would be so much more convenient as a router feature