Publishers are hopefully smarter than to bar people from playing the games they already own for no other reason than because they are scared people won't buy their new game. Anyone who doesn't let BC work for old 360 games will garner a lot of bad press when the feature launches considering everyone knows all it takes on their part is giving Microsoft the OK. They aren't new versions of the titles, it's simply letting you play the discs or digital versions on the Xbox One. If you don't already own it, you can buy them from the publisher, and they still make money without having to do anything. There's no loss to the publisher here at all, if they think so, they are stupid and anti-consumer.
Which is why some people are skeptical that many people will receive 100% of the Xbox 360's library.