I was thinking that the race would be orc, but on second thought, that might not be very feasible, if you consider a few factors:
-I am going to give the developers some credit by assuming they realize it doesn't make much sense to have orcs mingling with their natural enemy, the human (or elf, for that matter) and therefore these orcs would not be capable of going to human/elf towns, which means...
-Orcs obviously must mingle with orcs, which creates a sort of faction system similar to WoW(this doesn't have to involve PvP, but can, which means it can work in both Trammel and Felucca). I honestly can't imagine the developers going in this sort of direction though.
So now my new guess is gargoyle, because not only does it appear to be a highly requested race, but there is already a gargoyle city, and gargoyles (except for the rogue ones in the wild) are friendly with humans/elves.
On another note, there is no way the new race could be dwarves, or anything outside of Ultima Lore (by this I mean, races that don't already exist in game). It has been stated that the devs are going to be putting more "Ultima" in UO, so I highly doubt it will be anything that doesn't already exist.
Still we loom in the mists as the ages roll away,
And we say of our folk, "they are here!"
That they built us and they died and you'll not be knowing why,
Save we stand on the bare plains of Wiltshire.