This ties in well with the proposed authentication system and groups. Similar to the "special" Disconnect group, the reservation system could use another "special" group called PleaseDontKickMe let's say. The reservation plugin would ignore any players in this group when picking someone to kick. This would easily allow you to immunize people by IP address or steamid or whatever other authentication plugins you have running.
The group-based authentication system opens up interesting new ways of doing things, ways not easily done in the old AMX Mod X universe.