It's a good idea, though I suspect most people wouldn't use it, as it would be too much effort. It would allow people to set up worlds based on certain scenarios, like USSR, only using their planes. I'm not sure how difficult it would be to implement...
I think the best way to implement it would be to allow world owners to uncheck companies first, and individual planes by going to a separate page (or perhaps expanding a panel) for that company. I suspect most people would only want to select certain companies. Ideally the list of companies/planes to select would be only those aircraft in the world during the time specified for the game.
