I think this is a nice idea. Even better would be to return a DLite instance if possible, when using DLite, but that's beyond this issue, I think.
Also, it shouldn't matter if it's an AttrDict or a regular Python dict. AttrDict is just a wrapper implementation for wrapping a standard dict in a pydantic BaseModel.

I really value backwards-compatibility and don't like changing the system if we can avoid it. What might make more sense would be to provide an optional keyword argument to the .get() method that then allow the user to make the return output an AttrDict. Indeed this could be a very nice option as we could even add support for other datastructures down the line

In that case I will suggest to add a new execute() method with the new behaviour and deprecate get(). I anyway thing that get() is a misleading name of this method, see #108.

Note that the intention of this PR is not to ensorange people to put a lot of stuff in the session, but have a standardised way to e.g. getting hold of the collection_id. For this to be really useful, it should be possible to configure oteapi-services/otelib to use a given storage backend for all instances.