why do we need this? Mongo (3.4) is now doing graph and will also (obviously) do document and key-value. Is there something special about the storage engine, fo

why do we need this? Mongo (3.4) is now doing graph and will also (obviously) do document and key-value. Is there something special about the storage engine, for example, that will make this awesome for range queries (contiguous location ala RIAK TS or Cassandra rows)? Does it optimize for the new SSD controllers that have order of magnitude higher random read throughputs? Does it leverage GPU RAM? Does it occupy some barren area of the CAP triangle? Does it do something new, or is it just another neat query language on top of the same old storage algos? The "3-in-one" pitch doesn't fly for me unless the underlying storage tech does something special.