I have already realized that Orchard team is frequently looking at Drupal.
Drupal has taken the MVC way some years ago if I am right ? but there are many other CMS still not using MVC, just like dotnetnuke and they have a solid offer based on classical ajax+asp.net, with hundred of modules providing a great extensibility.
May be you should define what you mean by extensibility, I may have misunderstood your intention ?
I also would like to understand what you want to get away from, and who is 'we'.
I am not simply talking of web 2.0 but the recent 5 years extensions in the concept of CRM and entreprise: Paul Greenberg, one of the tenants of concept is here http://the56group.typepad.com/pgreenblog/2009/03/crm-20-social-crm-do-we-have-it-yet.html
If you are not familiar with it is a very solid move, not only dedicated to business. If the 2.0 term is not Ok for you we could also use Social.
And the name is not important, it is the sharing and interaction process driving the definition of products.
Not only marketing , many successful startups and companies are applying it. (Noisette devrait :) )
From my first month with Orchard, it certainly needs a solid marketing effort....
I have always see re-engineering as one of the software option: either you evolved an existing base code, either you rewrite to find shorter and better ideas and implementations.
Wording is not my best quality, especially in English as you may have understood :), I could do a try in Latin (for the marble it is better)