Points well taken. Like most conlangs, the creator or a small committee is the 'gateleeper' that approves new words. David is holding words back for some reason, and the major reason might be a legal one (I'm not faulting DP in any way for doing this). But if you look how Klingon and Na`vi have grown, it is because there is a community that actively uses and extends both languages. This, in turn benefits the people who make the films, etc., as the community has helped stabilize the base for the language, and as a result, the language takes a more prominent place in the ongoing story.
I certainly hope that David will continue to leak out details about Dothraki as he can, like Paul Frommer did with Na`vi.
I had revisited this thread before starting a new one, to see if a little more information was out there regarding the grammar, phonotactics, etc. I'd like to try building a few sample sentences, but have doubts that would be even remotely grammatical at this time.