A build server for Mac

I would like to see a build server for Mac to enable building iOS apps from multiple clients and remoting of the iOS simulator. 

Is it technically possible? Is it simply a licence problem. That is, Apple being 4 years old about it?

Do I need to write one myself... :)

EDIT: confirmed that xamarin ha "no plans" to support this quoting Miquel himself. 

It's still the licence fee and the need for one Mac per developer that is the hardest part for me as a consultant when I try to sell app development using xamarin.