Interesting idea, but I do not think that most magics are inherently good or
evil. For example, Pythium is definitely a holy, good nation, despite having
strong astral, and Abysia is an evil nation despite having elemental fire.
I think you are better off just choosing an era (for example MA) and a theme for
the fight, for example [RACIST HUMANS] vs [DEMONWORSHIPPERS] vs [NON-HUMANS]:
[img]/threads/images/Graemlins/icon17.gif[/img] organized, lawful, good to their people, but hate non-humans
Pythium, Marignon, Mictlan, Arco, Ulm, etc...

think humans are cattle and use them as such:
R'lyeh, Abysia, Pangea, Vanheim, Jotunheim, etc...
[img]/threads/images/Graemlins/icon27.gif[/img] want to subjuggate humans, but abhor demons and blood sacrifice
C'tis, Shinuyama, Eriu, Bandar Log, Caelum, etc...
They should start at war... write some history why it is so, and why no peace is
possible. Allow trash talking on the forums... and make damn sure that players
understand that they are supposed to HATE, HATE, HATE the enemy, and while it is
OK to gang up on the current leader, backstabbing the third party for immediate
advantage is righteous and encouraged.
Use a random map with about 20 provinces per player. Yes, that is big, but
remember, the win condition is one faction remaining, not one pretender.
Let people start randomly, and the in-faction communication and planning
will be a great advantage.
Or alternatively, make a custom, wrap-around map, and have each faction starting
together, but in possible contact with other factions. It's tricky, but far
from impossible.
By the way, I think that if this game ever happens, you better make sure the
teams are right from the very beginning.