PC support should be a no-brainer technically...presumably they've already done work on every single BC game to make it work within a wrapper (maybe an oversimplification, but you get it) on XBOne, the adjustments from there to much stronger hardware on PC should be straightforward. Releasing third party games from publishers that might be cannibalizing their PC port sales, on the other hand, is probably a serious roadblock for that functionality. Publishers who chose to allow their games to be BC on XBOne are almost overwhelmingly those who had no plans to do remasters and sell more copies on modern platforms, but PC games sales are another question completely. Lots of game ports from the 360 era can still sell for $20-$50 on steam, that would be a significant financial decision for every third party publisher who has PC ports.