Xbox’s disc-to-digital program looks like it could be a vital step forward for players who want to hold on to their physical games in an increasingly digital world, but it does have limits. Not every game publisher is on board with it, it seems, as Xbox users are reporting that four of the biggest companies aren’t “participating” at all. So far, it looks like games from Sega, Square Enix, Ubisoft, and Bandai Namco are largely incompatible with the disc-to-digital service.…