It seems that Traversable is doing two things:

1) Changing the shape of a data structure.
2) Folding over the contents of a data structure.

Traversable requires Foldable to enable 2, but Traversable is also applied to types such as (,) where only 1 is relevant.

If this is correct, follow-up questions would be:

1) For educational purposes, could these concerns be split without substantial drawback?
2) For practical purposes, could this be done without breaking a lot of existing code?
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