Even if the developer agreement wasn't there, the limitation is in the API endpoints (like andypiper said) and there's nothing we can do about that other than waiting very patiently.
(Also, general reminder that twitter is relatively unique in this level of openness, with an extensive, well documented and public API. And most competing services in the group conversation area have awful closed protocols. Some of them even decided to get rid of the "open" way to access it. So, if anything, I'm thankful that this is a "not yet")