The design for the Steeles subway station accommodates a centre median BRT on Steeles.
York Region and Toronto share costs of Steeles evenly, but the road is built to Toronto standards and maintained by Toronto. Toronto is about to start widening Steeles in the east end out to the Durham border, and is splitting the cost 50/50 with York Region, even though Toronto is the one building it, maintaining it, and operating transit service on it.
Now that I think of it, Brampton maintains and operates Highway 50 as well, with York Region cost sharing it. York region seems to be getting a good deal on both of their primary border corridors.