Insanely Twisted Shadow Planet has received a great deal of great reviews and if for whatever reason you've been holding out on the chance it's announced for PC then this is about as close as you're going to come to that without an official press release. A PC version of the game has been rated by the ESRB.
That on its own would put it in the "probably" list, but there's another little addition. Extraguy reported on the ESRB listing and the official Insanely Twisted Shadow Planet Twitter account retweeted it, adding a wink – ;). If that doesn't entirely confirm that it's on its way, I'm not sure what would.
Insanely Twisted Shadow Planet is an exploratory game that has you solving puzzles. It was released on Xbox Live last year to the excellent reviews that these sorts of arty games usually get and has since been long awaited on the PC. Expect an official announcement over the next few months, if not weeks.