According to NewType magazine March issue, director Imaishi Hiroyuki has announced his new anime project. The production studio is Trigger, a new studio established by Imaishi after he quit Gainax. Imaishi said he has been working on the project since 2010 along with Panty & Stocking with Garterbelt. Details of the project will be revealed in the June issue of the magazine to be released on March 10th.

Update (May 9th 2013):
The new anime will be a 2-cour TV series named "Kirurakiru" (Kill la Kill).

Update (Jun 30th 2013):
Confirmed to start in 2013 October.

More information can be found here.

Source: Scan of NewType (with a rough concept illustration)

Kill La Kill on MAL