I rather doubt we'll see a HTPC from Microsoft- it looks like MS is having a hard time getting the X1 to be half as good at media as the 360 already is. I don't think they'd split up their resources. Also, the X1 needs all the sales it can get, and the home-theater aspect of it was a huge selling point. I don't think they'd make a product that would literally be competing against the already underperforming X1. Furthermore, a lot of manufacturers make cheap, small HTPC boxes that run Windows. A) You'll be able to upgrade those to 10, B) a lot of OEMs were not happy that Microsoft started their own surface line, starting a HTPC line would not be profitable enough to warrant stepping on OEM shoes even harder.
Last, if they did have something I think we'd have seen it on CES already.