We have a webapp as our WME. But, at least in my experience, it is very buggy sometimes and consumes lots of RAM. I believe there should be a desktop app (mind you, not just a iframe in a exe, but a quality app) since it would be faster, snappier and easier. Regarding extensions -- I think they should be a part of the WME, not just a addon. It simply doesn't make sense to have to install dozends of extensions to have a better environment if it could be integrated.