There is a node in the Civil 3D Toolkit that will add additional types to the dropdown. It’s called DocumentExtensions.AddNewTypes. You might give that a try if you haven’t already.
As you probably know, we’re in a bit of an awkward phase right now with Dynamo for Civil 3D because there are a lot of core object types that have not been implemented. Paolo has added several more object types with the Civil 3D Toolkit package, and then I added some more on top of that with Camber. So if you duct tape everything together, you get a somewhat complete list of objects to work with. Paolo put everything in the Civil 3D Toolkit under the Autodesk.AutoCAD.DynamoNodes and Autodesk.Civil.DynamoNodes namespaces, which is acceptable given his position. But all of the objects in Camber are under the Camber.AutoCAD and Camber.Civil namespaces because I really shouldn’t be adding stuff to any of the Autodesk namespaces since I don’t have authority to do that (see discussion here).
So…all of that is a long way of me saying that I’m trying to keep Camber standalone and separate as much as possible from the work that Autodesk is doing (either through Paolo or the Civil 3D dev team). As such, I’m going to steer clear of adding any nodes to Camber that would do something similar to DocumentExtensions.AddNewTypes by adding Camber object types to that dropdown.
I agree that there are probably some improvements that could be made to filtering a selection set of objects, but I personally don’t think it is too much hassle to either use the All Objects of Type node or take a filtering approach using List.FilterByBoolMask or List.RemoveIfNot.