This is a nice idea, I'm just afraid how useful it be at the end. Personally I'm afraid of such solutions. Provide the model and then a tool generates few thousand lines of code. Working with such a monster at least for me is a nightmare - touch one thing, another breaks, then the upgrades come... I also usually decide to change the model later, but I already have a lot of UI and other changes. The tool will most probably will override something... And last but not the least this is hardly going to solve the main question - "How do I extend ...".
About your points:
1) Business logic - there are events coming in Sitefinity. This will help everyone to extend the BL much easier.
2-4) Regarding performance - artificial types are performing exactly the way the statically compiled do. OpenAccess generates the classes in the runtime, so they behave exactly the same as the static ones. Get/SetValue is not that convenient as the statically compiled classes and here Thunder will try to help.
5) About the backend extensibility - we're now working exactly on such type of articles - "how to ..." add button, link, column, etc.
We'll be happy to hear other customers on this topic and their ideas too.
the Telerik team
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