upstream copy= kwarg from sunpy to control whether view or copy of cube #1014

Yeah we should definitely upstream the kwarg, the issue is perhaps a question of defaults.

We need copy=True in submap here to preserve current submap behaviour, plus it just makes sense really.

Do we want to keep that behaviour in ndcube, where it is a change in behaviour from the current effectively copy=False cause cropy/crop by values are views into the parents in ndcube.

Both copy=True and copy=False have performance issues in terms of A) duplicating large data which is more relevant in ndcube than map B) keeping parent data alive when it could be discarded.

I can upstream it right now if we want the defaults to be the same (copy true) otherwise it isn't urgent but we should still do it as its useful.

Originally posted by @alasdairwilson in sunpy/sunpy#8843 (comment)