Well, one of the reasons for the question was, and maybe I have the details wrong, many veteran coaches asked for a world of their own when HD was changing to 3.0. Maybe they just wanted a 2.0 world. Can't recall.
I don't think ALL would fill but, given a month, I wouldn't be surprised if 250ish spots could be taken. Users in different worlds, who would like to compete with one another on even footing, would be afforded that opportunity. Nothing motivates sim users like "new". And, of course, you have the whole bragging rights thing. If the guy dominating Smith thinks he's the best and the Rupp, Iba guys think the same thing, there's their chance to prove it.