If locking and pushing/washing out the front weren't a thing, then neither would ABS be a thing. Shimano evidently thinks otherwise and filed a patent in 2019.
https://www.freepatentsonline.com/y2019/0233049.html
Even before Shimano, Bosch and Blubrake had ABS systems on the market for e-bikes. Shimano no doubt intends their system for the e-bike market, but the language in their patent intentionally includes other types of bikes including, "a road bike, a mountain bike, or a cross bike”. E-bikes are the natural initial target for ABS systems since they will require a source of electrical power to drive the controller and the pump/valves, but as Di2 systems become more prevalent on non-e pedal bikes, a substantial auxiliary power source for more than just lights will pervade there also.
The bottom line is ABS and electronic traction control are coming to bicycles of all types, and similar systems on motorcycles have already proven that maximum braking and shortest stopping distances are achieved with the combined/integrated use of both front and rear wheel brakes.