Regarding our wonderful doc on multi-location documents for 2D indexes:
http://docs.mongodb.org/master/core/geospatial-indexes/#multi-location-documents-for-2d-indexes

There is no equivalent document explaining how to do this in 2dsphere indexes.

A 2dsphere index achieves the same effect via the use of "MultiPoint" GeoJSON objects, which is a sufficiently different mechanism as to not be immediately obvious for people who are upgrading from a 2D index. It might be nice to call this out on the above document.