Propulsion for the 2030/40s

The prolific Dave Majumdar on the DEW line blog has posted on the initial rumblings for the FA-XX propulsion:

http://www.flightglobal.com/blogs/the-dewline/2012/04/propulsion-key-to-fa-xx.html

Similar thoughts must apply to UCAV and potential Rafale/Typhoon replacements….

What is the fast jet propulsion of the future?