Deprecation of Panel ?
This is a topic that has come up recently (https://github.com/pydata/pandas/issues/10000, https://github.com/pydata/pandas/issues/8906, pandas-dev mailing list discussion), let's make this an issue to track the discussion about it.
- https://github.com/pydata/pandas/issues/8906#issuecomment-152613473 experience of the 'experimental' status of Panels by @MaximilianR and following discussion on pointing users to xarray
- Issue for docs on using xarray instead of Panels: https://github.com/pydata/pandas/issues/12283
- "WIP for transitioning from Panel docs" PR https://github.com/pydata/xarray/pull/832

Deprecating Panels would be a rather large change, so:
- Do we need to further discuss if we actually want to do this?
- Are there people who make intensive use of Panels to ask feedback?
- How do we go about such a deprecation? First making a note in the whatsnew / pinging mailing list or other fora before actually deprecating?

cc @pydata/pandas @MaximilianR 
