Best way to scale large number of manager users

My situation is: The organization I’m developing for has chapters all around the country. They currently only have about 10 chapters, but are pushing hard to have 50 within the next year and 500 within 5 years.

Currently, I have contexts setup for each sub domain (each chapter has its own subdomain). The chapter administrators are only allowed to see their current context when they login.

My question is - will this approach scale or do I need to implement a different strategy? One obvious step would be to setup user permissions so that the full resource tree doesn’t load in any context - but I’m not sure if there might be other issues. Does anybody have a similar scenario? How are you managing this?

I know there was a thread about this a while back, but I can’t find it and I don’t recall that there was a recommended approach given.