I'm working on an interesting project right now where the web application behaves like a typical SaaS solution, except that all of the customer's data is hosted

I'm working on an interesting project right now where the web application behaves like a typical SaaS solution, except that all of the customer's data is hosted on premises. After the initial install, their local servers (and data) don't have to be touched, but the SaaS portion can be continuously improved. So far it's worked really well. Your MSaaS idea sounds really interesting, especially the multiple trusted deploys. That's the crux of trusting deployed open source software.