Do you think Sam Langford gets to break the colorline? Would a better liked fighter breaking the colorline do more to advance black fighter? Or would him breaking the line make him hated? Would this increase Langford's rating? How long would he keep the title? Or would someone else win it instead? Would no one else have forced it enough to break the line? Would the white hopes instead have been a series of lacklustre champions? Or would one or a few have stood enough to be highly regarded (Frank Moran maybe later)
I suspect that Burns would eventually have cashed out against another black contender, most likely Sam McVea. From there things could get a bit sticky!
Im going to go out on a limb and say that Burns reigns longer than expected (he would have done fine against Johnsons challengers) and the knee jerk reaction to pick Langford as the logical next champion isnt as much of a lock as you might think. However, I think if the color line is going to be broken it would be Langford who did it. He was popular enough and his life wasnt as threatening to white America as Johnsons so there would have been good will and support for him and he was also a good draw. I think an eventual fight between he and Burns, or a series would have been very interesting.