SunPy Proposal for Enhancement 12: NDCube 2 (SEP 0012)

This SEP proposes a redesigned API for the NDCube class and its associated classes in the next major version of the ndcube package. The primary objective of this SEP is to gather as much community feedback on the proposed API before it is released. This is also a prelude to a future change, long discussed, to have the GenericMap class in sunpy core inherit from NDCube. This SEP should therefore also be considered as a discussion of future changes to the Map API, as the API proposed here would eventually (with long deprecation) be adopted by map for the functionality provided here. That being said, details of the migration of Map to this API are out of scope for this SEP, just a discussion of the eventual API to be adopted.