Ok, the OP and you have two different ideas of what nested bases means and this is what I was concerned about.
OP seems to want a bases of bases, where each “child” bases have attributes testable against the parent base attributes.
Right now, bases have no intrinsic attributes, aside those coming from being files (like creation date). It isn’t clear to me how this would be useful without first extending/exposing the bases attributes. To the OP, you can open a FR and try to be as clear as possible to what you want and why.
@mbhutton What you are describing is not nesting of bases, but the intersection of bases (views) within the same base.