I don't know why anyone would even consider replacing the rock solid 722.6 with a 722.9 which is much less reliable.
Maybe for the same reasons they replace comfortable and safe 16-17" wheels with low profile - tooth grinding 20's
The subject of swapping parts of drive-train on digital cars come pretty often.
Everything is doable if time and money is no object.
I know blog of Polish guy actually converting 603 mechanical diesel into digitally-controlled, turbo engine with matching 5-speed electronic transmission.
Reading the blog, the fact that W124 had reluctor rings with different number of knobs to work with 5-speed was his biggest surprise.
Coming to adopting one digitally controlled piece of equipment to different car.
I like to watch "Fast and Loud" - the program about top-end car restoring and converting shop. In one episode - (tried to find episode on youtube, but found promotional clip below) , they put racing engine from one car into classic hot-rod.
In the process they remove about 50 lb of wire harness, as they did not have electric mirrors and sunroof on the clasic.
So those top-end professional mechanic could not make the car computer talking to the "motor".
They call hyper-duper car technician and few hr later no dice.
Than come super-hyper-duper team of racing technicians who after several hr of work make the connection.
So if it took 3 levels of the best technicians in the country to make US engine to talk to its converted computer- imagine what DIY can face.