Seems like a good fit to me. ESRI doesn't have any investment in the Python language or community. I think the company simply chose the language with the least syntactic distance from Avenue. I've been following news of IronPython since Hugunin switched to it from Jython. This was prior to his hire by Microsoft. I have not yet downloaded it to confirm directly, but I expect that it would be -- via the CLR and COM interop -- a better bridge to all the COM in ArcGIS than is C Python.