I would start by not building a web 1.0 style framework. We are in the middle of a transition to richer browser based applications and server side, non-standard

I would start by not building a web 1.0 style framework. We are in the middle of a transition to richer browser based applications and server side, non-standard web technologies like PHP, ASP, JSP, Servlets that spit out HTML are being passed over for straight HTML, JavaScript, CSS and XHR calls to the server this is a good thing because it simplifies the stack significantly. If I where to build a framework now, it would be a framework build on one of the JavaScript toolkits (at least pluggable so any of them could be integrated, If I had to chose one it would be Dojo or jQuery depending on what I was targeting), a REST library, a content based router and a security API. I would also consider bolting on a CMS that templated HTML and exported it to pure HTML on a web server. This is where the future of the web is heading to build another ASP.NET or PHP or Struts on Node.js will give your product a limited lifespan.