Can anyone tell me why Cvet's SDK isn't developed?
SDK was actually updated 13 minutes after you posted your question.
(and the update is really cool - it is a heavy optimization of 3D model rendering)
Updates should be coming more frequently now, since Cvet is working on a
new project* on the engine, and the engine is being heavily improved.
*sorry, the website is only in Russian at the moment, but screenshots should be self-explanatory.