concerning the migration phase:
- do you have an idea of which applications make use of it? (asking in case you have some idea, but likely we cannot be sure of all of it)
I remember working on a game but I forgot the name. Generally it's DRM schemes that try to bind an account or install to a particular machine.
- a countermeasure could be to set a flag in the Wine prefix (dont_hash_machineid, at value 0 when not defined) to control the activation of the hashing ; every new prefix would be created with the flag set to 1 ; that would limit the impact, but not eradicate it (if user reinstalls his/her app in newly created prefix) ; that could eventually controlled in winecfg with more context on the pros&cons
I don't think we'd want such code in Wine.