Create class for instantiation at runtime

[The trick]

Ok, another question. The DispID value that's in METHODDATA, those are just arbitrarily assigned so that IDispatch knows what to do?

Yes, excepting the some values.

The fact that we must be so careful about teardown makes it seem more complex than just creating more CLS modules.

You just need to create the some precompiled-thunks for the IUnknown implementation which check if the code is running and delegate the call to the code if need. There is other thing. You can't just replace an UDT with an Object because that's the different entities. For example, when you assign a object variable to other one it just calls AddRef (or QI if different interface); when you do the same with an UDT it copies all the members of the UDT to another one.