Let's say, instead of 2-vs-2, the tourney was 3-vs-1, team partners are random, in-game teams are random.

Could that work?

Why?

for something like the Zombie Farm one....what's it called Walking Dead or something? 

That's one. My Ravenloft team map is another. I think there are other Nvs1 team maps as well.

What happens when four people are assigned to play each other? Would it be randomly assigned personas? Or four possibilities to choose from, so that whoever is quicker can choose between Strahd or a hero persona?

I would have to make it random assignments.

Interesting idea. I tend to be unlucky with teammates in randomly assigned tourneys, though, so I expect I'd be Strahd most of the time and be stuck with myself.