Once Keyman for Windows Engine is updated with the Keyman Core processor, there will be a period where either processor can be used via a Windows Registry entry most likely for the whole version 15 time period. See issue #5011 Once sufficient testing and stability is achieved the windows processor code shall be removed. This Issue is created to make sure that happens and provide information to help achieve that goal.
Searcing the code base for "TODO: 5442" will find places that have been marked for removal. This will not be a complete list of all places but help insure dead code is removed as it is easier to mark this now while working in the current 5011 issue.