@fitze Hi We discussed to include this method, for nesting vframes, to allow complex shapes for some objects.
But I feel it wont be needed with the new API.
@moorepants I will explain a little bit here.
Why we wanted this method in first place.
We wanted to account for creating complex shapes as a combination of vframes which had simple shapes.
They could be tied together, and could be animated together as one single unit. It required specific arguments(numerical values), for that specific parent frame, which would allow all children to be attached together (in visualization) and move together.

Now even If we dont have this nesting to be allowed, since we are only supplying same set of numerical args (integration values of p's q's and static values of mass etc.) there is no concept left for specific arguments for different visualization frames.
That was certainly a different approach for evaluating numerical transformation matrices, and for the current approach it doesnt seem to stand anywhere.
I would also describe, for clarity, the specific arguments which would have been required in the earlier approach.
Like we have a set of nested frames, for representing a RigidBody, then the specific arguments may have been say mass center values at different times. But now it is not needed.
If you have other ideas please let me know. Otherwise we can discard with nesting of vframes altogether, and I feel it wont affect anything on our project.