This works correctly from 2.4 -> 2.5.3. It begins failing in 2.5.4 and is still broken in 2.6. Server ticket SERVER-9341 seems to indicate this is not supported, but our documentation indicates that geoJson is an accepted format for 2D indices. In addition, since this works correctly in 2.4.10, it seems that this should continue to work; otherwise it is a backwards breaking change.
Error Message:
QueryFailure flag was Unable to execute query: error processing query: ns=milieu.venues limit=4 skip=0 Tree: GEONEAR field=location.geo maxdist=1.79769e+308 isNearSphere=0 First: notFirst: full path: location.geo Sort: {} Proj: {} planner returned error: unable to find index for $geoNear query (response was { "$err" : "Unable to execute query: error processing query: ns=milieu.venues limit=4 skip=0\nTree: GEONEAR field=location.geo maxdist=1.79769e+308 isNearSphere=0 First: notFirst: full path: location.geo\nSort: {}\nProj: {}\n planner returned error: unable to find index for $geoNear query", "code" : 17007 }).