For the next SharePoint version, I will bet on ASP.NET Routing as a main technology adoption. Upgrading VirtualPathProvider implementation would benefit the platform in many ways, even the following adoption of ASP.NET MVC.
Today I remember my main wishlist: friendly urls.
http://server/blog/posts instead of http://server/blog/_layouts/listfeed.aspx?List=<GUID
http://server/services/docid/CUSTOM-1-1 instead of http://server/_layouts/DocIdRedir.aspx?ID=CUSTOM-1-1
It would be great to have friendly urls for services (example Document ID), or RSS Feeds or <put your requirements here>. Of course it should consider extended managed paths for keywords or services and the adoption of some existing de facto standards (microformats).
In this scenario I would recommend reading Windows Live Lessons learned in the adoption of ASP.NET MVC
moving to a RESTful world?