I like allot of the ideas so far and also agree that persistent worlds, large player counts, major on the fly changes, etc. are most likely "out of scope".
I feel that even dedicated servers are out of scope (never intended), but I still hope they are considered. Think of the issues you face if the host crashes mid game, they suddenly need to leave, or the machine they are on has trouble hosting. I think some people would like to be able to GM and/or be a player on their own server as they see fit. Maybe even switch roles during the same play session.
Also most people these days don't seem to want to stick around for very long play sessions so a friendly drop in/drop out system is a must. I think that dedicated servers would certainly enhance this.