OpenWrt is by far, the best router firmware that I have ever used; however, there are a few features that would make it just that much more complete...
It would be nice, if the Overview page in LuCI could kick / ban users from the network. Of course, a user management page, under the Network tab could have more detailed features, like setting the amount of time for a ban(s), and perhaps an ability to promote / demote users in accordance to traffic priority.
Having WPS push button within the Overview tab would be ultra cool too.
Third, an ability to set specific lease times for guest devices within LuCI would be nice.
Lastly, if there was a way within LuCI for guest devices to only be assigned IPs within a specific range, that would be superb.