The Geocaching Weekly News Letter of April 21st carried an article informing of Groundspeak's decision to place a pause on all Challenge Cache submissions [for publication] for twelve months, effective from 21ST April 2015. This will not affect existing Challenge Caches already published.
Further information here in Groundspeak's Help Centre:

I just stumbled across this info tucked away half way down the news letter so felt it pertinent to bring it to members attention. I believe that Groundspeak are planning on garnering cachers thoughts on challenge caches, and also how to proceed with them in the future.

I'd be interested to hear other members thoughts on this.

Cache On!