What essentially is different from ACA500+ 2016 to 2018 ?

There are very minor differences - from the software side, everything is identical, so you can flash straight to the latest version.

First is the obvious one, the DisMo has smaller digits and the button in a different place. Features are the same, as it's the same circuit and even the same code that's running in the MCU of the DisMo. It just has a different identification string.

Second difference is that the CPU is the 68ec000 type, where the 2018 had the 68sec000 processor. This is a package difference, but the software won't see any difference, because the die is the same; some of these chips even have the same mask ID, indicating that the silicon is the same. Still, there's a chance that the 68ec000 CPU of a specific card will only run up to 14MHz, which is why the guaranteed speed has been changed to 14MHz. You can still choose up to 42MHz on the 2016 version - it's just that the guaranteed speed is a tad bit lower than on the 2018 version.

The third and final difference is that the "resistors of shame" are not there on the 2016 version. These only come into play when the user makes a wrong connection - mostly when connecting to non-recommended computers auch as A1000 or inside case contraptions that use funny adapters. This is not a functional difference either, but it's for limiting the amount of damage that is done by such a wrong connection.

The reason why we went back to the 2016 design is of course chip shortage. I may have to make yet another re-design to use 68HC000 CPUs and a different MCU for the DisMo, as these parts are so hard to find these days. The biggest task is to keep the cost within acceptable limits, which is becoming an increasingly difficult problem, as Motorola CPUs are a finite resource.

Confirmed.