I am not sure if this is a good idea. Creating different AppDomains in one process is a little scaring. Do not know how to catch thread level exceptions for each domain. It might be possible to do it. Have not tried. And another thing is how to handle threading context. Not sure. To be honest, I did not we could have different App.Domain in one process. Let's find out more about App.Domain.
===later added
By reading a little bit about App.Domain. I think it might be a good idea. Process is a concept of Windows OS. App.Domain is a concept of .Net Framework. It is about CLR running time resource. It might be good to separate AppDomain for different services.