Siege: Clan War did an acceptable job within a story line approach.
That's a boxed game, right? I mean, essentially -- comes with decks designed specifically for it?
It's much more restricted in a variety of ways; probably a bad example to draw from.
I'm not much interested in 3v1 multiplayer, though Star Wars did it in their 2nd deluxe box (along with 2v2).
I think a fundamental requirement for multiplayer is good free for all. Anything after that is gravy. Special formats requiring additional cards should probably go in a separate deluxe box, perhaps with a handful of exceptions. Certainly a siege deck should be in a supplement.