Clojure static typing

It certain possible. However I do not think that Clojure will ever get any form of weak static typing - it's benefits are too few.

Rich Hickey has however expressed on several occasions his like for the strong, optional, and expressive typing feature of the Qi language, http://www.lambdassociates.org/qilisp.htm

It's certainly possible. The compiler already does some static type checking around primitive argument types in the 1.3 development branch.

Yes! It looks like there is a project underway, core.typed, to make optional static type checking a reality. See the Github project and its documentation

This work grew out of an undergraduate honours dissertation (PDF) by Ambrose Bonnaire-Sergeant, and is related to the Typed Racket system.