TK confirmed today on the Third Wire forum that his development team has indeed been working on a WWI combat flight sim.
There's a few scrolling teaser shots of a Spad 13 on the TW homepage, and you can read this thread here for a bit of an idea of the design approach being pursued for the game:
http://bbs.thirdwire.com/phpBB/viewtopic.php?t=1463
You may have to pinch yourself, but it's true, a serious developer is finally looking to do WWI!!!