I don't have all the answers to your questions. I have tried side-loading the IPMA software from newer Navigators onto a 2022, but was not able to get it to work right. What I can tell you is that any vehicle with the hardware for BC 1.0 can also run 1.2, 1.3 or 1.4. I know for a fact, because my F150 has had BC 1.0, 1.2 and now 1.4 (the trucks were skipped over 1.3) and they all work fine.
The new Mach E with 1.5 for sure has a different IPMA with a 5th strategy location and TRON encryption in the IPMA, so it is unknown if we can run 1.5 on the hardware we have. The TRON part is not a big deal, but the 5th strategy is. What I can tell you is that the current IPMA found in 21-24 vehicles has the config built into it for the auto lane change feature in BC, but it will not perform an auto lane change if enabled it. So the config is there, but the event itself does not exist in the IPMA or the event is not supported by the GWM. We tried side-loading the 1.4 software onto a 2022 Navi, too, and the truck was not happy. After playing with the config, we were able to get predictive speed assist to work, but lane change assist and in-lane repositioning buttons would not turn on. However, lane change assist would work even though you could not turn on the buttons, but there were constant hard faults on the dash.
What is interesting about the newer Navis & Expos is that the IPMA software they have for BC 1.2 is the BAE strategy which is the same software 21-24 Mach E's have and Ford calls it BC 1.3 on those cars.