I don't think there would be an issue with activity. That just sounds like a really lame excuse for developers to not pursue this. If a system were to actually be created for it, all that would be necessary to create activity would be the announcement of the rehaul in the news. Just look at what happened when they announced the new GS stuff. Lots of veteran sparrers were actually afraid Belle Spar was going to "die" because of how many people started sparring there. I mean, sparring at Belle has always been around and it suddenly gained TONS of activity just because they made one minor addition to it and announced it. The soccer arena would just have to be enjoyable enough that a decent number of people actually stick around and continue to play even after the initial few days following the announcement.