I have suggest the UI map like two years ago.
Personally it was my favorite Ultima map. Too bad it was destroyed. Doubt it would ever happen though. It is a too huge map for any playerbase, no matter small or large. I mean we need at least 800 of active players in order to make that map effective, with 200 players covering each of 4 continents.
Ultima I and III maps as well as other Britannia versions are actually available on the dark shard project:
http://darkshard.net/basic_maps/index.html
Not sure if they could be converted to alpha grahpics though.
What I suggest is adding just one Dungeon (Despise) and the dungeon surrounding area as well as just one additional town - Yew. And the area surrounding Yew and the crossroads.
That would be more than enough. Though I like the just Britain concept, it makes it feel more of a town-domination gameplay, where each player faction is aiming at taking control over Britain, another town would be also useful to make a trade between the cities provided that there are more region-based resources available on the map. Such as, Yew wood could only be harvested in the Yew Deep Forest, no where else, and Iron could only be mined in the Britain region, thus woodcutters from Yew and miners from Britain would have something to trade between each other. One dungeon would also attract more players and guilds to take over big spawns. I think everyone would agree that Myndon maze is just not enough anymore.