I wonder if Umbraco 5, which is based on MVC, is appropriate for a Line of Business application, mainly to handle extensibility.
Would it be a good ideia to use Umbraco as a base, and create modules to be installed on it?
Does Umbraco use MEF for extensibility, or something similar?
Note: I don't have any experience with Umbraco.
as you properly know umbraco 5 is only in beta mode atm..
but umbraco 5 looks really promising, you can read some of umbraco thoughts about MEF here