I thought it had been released, at least through their KS, and that there was also a previous beta-version circulated on PDF?
Edit:
We have now (July 2020) successfully completed fulfilment of all three hugely successful Kickstarters for War & Empire. We are now delighted to take this lovely new section of the range for Dark Ages, together with the War & Empire Rules to Retail release. Release date to be advised soon.
Seems like the rules went out with the KS some 18 months ago...? Covid notwithstanding, I'm surprised that nobody appears to have read them, posted about them, or even managed to get a game in with them.