Yes, an enddatetime would work. That's the solution I thought up too. But you can probably make it a low priority as I shouldn't need to do this sort of full request again. Once my code has a cached copy it will just request incremental data.
The parameter was added into the APIs. You can look at the docs.
Be aware that the startdatetime is inclusive whereas the enddatetime is exclusive.
So if you batch, the next startdatetime should be equal to the precedent enddatetime.
Apart from that we are moving some calls to memcached so APIs and other parts of the FrontEnd should work faster.