bramu: I'm curious what extensibility features you feel you are missing?
gouletf: We are well and alive. In fact we just released a 3.0beta that adds support for all the new features in ArcGIS Server 10.1beta (JS API doesn't have one API yet, so that's one hint that we are not slowing down or are behind). We will also have a v2.3 coming out shortly that will have features that the JS API won't have yet (but soon to follow). In other words, we are alive and well, and cranking out new versions for Silverlight, WPF and Windows Phone.
Don't read too much into what the rumours are around Windows 8. Windows 8 runs everything that Windows 7 runs, and that includes Silverlight and WPF (what you are referring to is the metro style apps which is just a different technology, but most business oriented apps fits poorly in that model anyway). We'll be building Silverlight apps for a loooong time.
