pydata/xarray as monorepo for Xarray and NamedArray

[dcherian]

What is your issue?

As we work through refactoring for NamedArray, it's pretty clear that Xarray will depend pretty closely on many files in namedarray/. For example various utils.py, pycompat.py, *ops.py, formatting.py, formatting_html.py at least. This promises to be quite painful if we did break NamedArray out in to its own repo (particularly around typing, e.g. #8309)

I propose we use pydata/xarray as a monorepo that serves two packages: NamedArray and Xarray.

• We can move as much as is needed to have NamedArray be independent of Xarray, but Xarray will depend quite closely on many utility functions in NamedArray.
• We can release both at the same time similar to dask and distributed.
• We can re-evaluate if and when NamedArray grows its own community.

[TomNicholas]

Another option would be to make the NamedArray repository a git submodule