Should copy() attempt recursive setalloccol?

[MichaelChirico]

Seen in this Q&A:https://stackoverflow.com/questions/62164617/reference-problem-in-data-table-following-a-copy

user needs to run setalloccol on internal data.table columns -- a bit obscure to figure this out on ones own. We could attempt some sort of recursive setalloccol (e.g. make the internal reallocate recursive or finite-recursive), but is that a good way to solve this? or leave it to end user to do this?