blizz has been doing the classic versions near last patches. this could mean the bracket you are targeting will not be 70-79, and could be 70-74 and 75-79. all the x9 brackets remaining other than 19s (15-19) died, other revivals failed. based on the way classic versions are done why not stay in WOTLK
blizz however has done some exceptions in regards to twinking like in WOTLK. they did not separate XPon and off. you may have a chance they do not do the split in CATA unless they get WBO's twinks to petition the split.
in Van CATA the basic game was still capped at BC, in the classic versions they are all separate, because classic players wanted separation. in Van CATA the three levels that made brackets active were 70s, 20's, and 19's.