Bart de Smet wrote a very interesting post about the possible creation of an Updateable LINQ provider, especially if it can be used for a SQL dbms (of course it would work with LINQ to SQL but it should be applicable to LINQ to Entities too). I like this approach very much.
However, a Microsoft word on this, especially defining the "official" LINQ extensions and interfaces to implement an updatable query provider, would be fundamental to write code that will be still valid when a different LINQ provider implementation will be used.