Steering by wire --> none of the cars you listed have steer by wire. Nissan is the only OEM who has steer by wire in production. Brake by wire --> does not exist at all.
You are right in the formal sense, none of those cars officially have by-wire functionality but in order to have LKAS, Park Assist and ACC work they need to support steering via can bus messages and braking via can bus messages. I used by-wire in an informal sense. Disclamer, I have never worked in the car industry, that's why my terminology is a bit loose.
Work on the Lincoln MKZ / Ford Fusion was made popular thanks to Dataspeed / Autonomoustuff, they open sourced a ROS module but most of their magic is propietary / secret. It's expensive but a lot of startups use it.
The work that you point to is what we now know "openly", and yeah, there is only a few of us and I am one of the firsts sharing their findings on that specific model. There are a ton of people who know what we yet don't know but they don't/can't share it publicly.
While no cars have brake by wire, the computer can stop the car using mechanical actuators already(ABS is exactly this, or the more modern emergency breaking system) - same with steering, plenty of cars have "parking assist" where they park themselves, so the computer must be able to control the steering even if it's done by mechanical means.
Every car that has an lane assistant or a parking assistant with automatic steering, and there are number that do support either of those, is having some sort of steer by wire. Even the lane assistant is normally designed to give you a force in the steering wheel to keep the lane. That you can reuse for automatic driving of some sort.