I got a little bit of clarification on scaling out Team Foundation Server on the chat this morning. Basically, it sounds like they just aren't planning for it or testing it. This seems odd to me for what amounts to an ASP.NET application being written to support hundreds of users. How does scaling out get pushed to a later release??? :-/
Obviously customers will end up testing this scenario for them, and as long as they didn't do anything violating MS's own best practices for web development, it should work. If it doesn't, I would expect MS to get verbally abused pretty bad for whatever design decisions prevent it.