I love the new profiling capabilities in Visual Studio, but there's still a gap when doing end-to-end performance testing and tuning. I'd really like to see the app get instrumented from beginning to end. While local devs won't see how constrained networks might affect their app, I think the perf tools can be smart enough to take the local tests and apply a few algorithms to show what kind of range of response times users should see, depending on their bandwidth and/or distance from the server. I know a lot of this might be a guessing game, but it'd be nice to at least have some numbers to see how big pages are and what user-focused response times are. At a minimum, I'd like to see the size of pages and the time spent requesting, processing, responding, and loading the page in the browser. Anything else would be icing on the cake. There was an entire office setup to do this when I was in the Air Force. Having it all built into the dev environment would save an immense amount of time and money; especially considering most devs aren't fully aware of all the factors that come into play and how they can tune their apps.
That kind of brings up another possible area of this end-to-end instrumentation. I'd like to tack on a best proven practice analyzer to the output that would make recommendations. Of course, not all recommendations are universal, but at least providing some pros/cons to each would give devs more info than they have right now.