Collections will no longer be dropped immediately with 2-phase drops (still in progress). Instead, the collections that the user requests to be dropped will be renamed to a non-user visible collection in the same database in the <db>.system.drop.* namespace (see SERVER-29251 for details on the drop-pending namespace). Eventually the hidden collection will be removed from storage when the rest of the replica set has progressed past the commit point where the collection drop can never be rolled back.

Currently the listCollections command should be excluding drop-pending collections from its results. If the user wants to see these hidden collections, there should be an option to listCollections to include these drop-pending collections.