Exposing Slate To Blueprints is possible.Apart from UMG i have just finished exposing some very basic functionality on blueprints i might add a textbox and some other small stuff for a simple UI, but it seems smarter to wait it out for the unreal devs to finish the UMG plug in.
On a side note though if you are a programmer i think its much easier and cleaner to stick to hardcoding your UI with Slate espicially if you want games like Flappy Bird. The same stuff they do on flappy bird with dozens of nodes can be done with 100 lines of code using Slate just saying 