I could not agree more.
We need to have the ability to edit or create our own checklists.
Or, at the very least, some documentation as to how the XML tags work in the current XML checklist files, so we could then edit them to our liking.
EDIT 2022-04-01
After further searching online, I did manage to find some documentation regarding the checklists on the SDK developer forum: https://docs.flightsimulator.com/html/Content_Configuration/Checklists/Checklists.htm