It's odd that Jeroen would mention this huge design gap and in the next breath invoke SDI and standards-based internet GIS (note that Jeroen, in his blog, often espouses rethinking SDI in light of the web).
GIS/SDI architecture design is to web architecture design as 18-button mouse is to "magic mouse". Buttons vs. gestures. A multitude of complex, specialized, rigid protocols vs. one dumb protocol that can channel different, complex, emergent interactions.
(Of course, it's hard to imagine that Apple is going to make it easy for mere mortals to create their own gestures, but hacks should be forthcoming.)