Haven't played the Warhammer Invasion multi rules, but I don't particularly like the SW multi rules. Team play is slow like molasses and involves too much shared information between teammates.
Invasion is actually quite good as a multiplayer game.
To be clear, SW = Star Wars. Just so no one's confused. I don't want people to think I said that I didn't like the Invasion multi rules in the same breath I said I'd never played them!
That said, I haven't played *much* invasion in general. To me, the main thing agitating against multiplayer would be the last man standing problem. Since you win 1v1 by eliminating your opponent, the natural assumption for a win in multiplayer is being the last one eliminated. To me, a good multiplayer game keeps every player involved as much as possible, which elimination games obviously don't do.
Strictly out of curiosity (I have no plans to start playing a game with so much extant product), did they address the elimination issue in Catacylsm? (That was the name of the multiplayer box, right?)
To bring this back on topic, 40k seems more naturally suited to multiplayer, because while you can win by eliminating your opponent, there is also an affirmative goal to achieve (winning 3 planets with at least one shared resource icon).
In fact, without seeing the card pool or full rules, it seems to me that multiplayer can be played with very few modifications. Highest number of icons present (or the only Warlord present) still wins command struggles, as is the case in 1v1. For actual battles, you can shoot any opposing armies in the same battle. Last unit standing wins the battle.
Everyone would be a little bit card/resource starved, since it would be dividing 5 planets' worth of card draw and resources 3 ways instead of 2. More players would also increase the number of Warlords that come into direct conflict, making elimination more likely (boo).
Not sure what other modifications would need to be made. We still don't know, for example, how to determine which player shoots first in 1v1, so it's hard to speculate on if the rule would need to be modified for more than two players.