Some thoughts about why the vacuum switch was deleted, just guessing.
If we think about the carby days, we had a distributor with mechanical advance, vacuum advance, and points. These parts would wear out and become increasingly inaccurate over time and use, and often fail. The ideal gradual increase in advance required for increased RPM is not identical to the gradual change with the springs in the mechanical advance, but it was considered good enough at the time. So they weren't even accurate when new. Computers can use sensors with fewer parts that wear out, and can be programmed to provide the ideal amount of advance. A vacuum sensor was used for vacuum advance. Then it was realised that the computer can be programmed to provide the correct amount of vacuum advance without a vacuum sensor, due to the inputs it gets from the hall sensors.
BMW often made parts backwards compatible, in this example there would be no need to change the part number, anyone wanting to buy an ignition control unit would be supplied with the new version.
In later models with a motronic computer, it was realised that the fuel pressure regulator doesn't need vacuum assistance to reduce fuel consumption in high vacuum situations, again the computer already has enough inputs to predict the ideal amount of fuel required, and provides it according to its program.
