Example 5 shows a worse problem in lanes:* from the possibility of using lanes:bus:backward=1 + lanes:taxi:backward=1 for lanes:backward=1 . I feel that simply the question of whether busway=lane is counted in lanes= needs to be decided. It can be preserved as a crude method when someone doesn’t want to do all the motor_vehicle:lanes= + bus:lanes= in different number of lanes= on each section. That would ease bus lanes on wider roads.
It could be applied non-physically separated center-running bus lanes Shouldn't we make rules that suit each country's road system?
Another application is determining the side of bus lanes. bus:lanes= would have to be parsed. With busway:*=lane , it’s straightforward.
In either case, you can instead start with deprecating busway=opposite_lane only. That’s as easy as cycleway=opposite_lane recently.