I think I can deduce why there hasn't been an announcement for adaptations yet (or what Brandon exactly meant when he said last december that it was about "getting it right)

I think it's all because the scope of the Cosmere and the quality control that Brandon wants, because for one thing, the Cosmere isn't something you just adapt like any book, it's a whole shared universe that has a specific set of rules that one cannot break, and of quality control, I personally think that it's possibly unheard of in Hollywood, and the studio heads gradually realized that as talks with Brandon happened, I mean, it's about using Brandon's vision, and the potential directors are probably gonna have to respect several things that maybe them and the studios will feel difficult to do.