Currently, OData supports atomicity strictly with a single entity or by the use of the $batch service.  The $batch service is great and has it's purpose but is very burdensome to implement.  A very common situation is to post a document (i.e. a sales order) with a header and line structure but require that it be posted in an atomic manner.  This can be done with the $batch service but only with a lot of additional work.  If we could use deep inserts to post the header and lines nested within all in the same operation without the need for additional overhead of the $batch service, this would be a huge gain and would get us much closer to what the AIF had available to perform.