We have now officially confirmed we are working on Xenonauts 2, and we're currently hoping for a 2017 release for the game!
The full statement and some basic details on the sequel can be read here (with more to follow in the next couple of months): http://www.xenonauts2.com
Thanks to everyone that has supported us by buying the first game - the experience we've gained making it and the feedback received from the community should allow us to create something even better second time around!