You can read the memo about it here:
Basically /.well-known/ is a place to check for common site meta data and you can suggest new urls that can be registered.
Has been accepted and added for the use case of pointing to where to change your password.
If you think this is insufficient then there is nothing stopping you from trying to put forward a more comprehensive proposal for say /.well-known/change-password-api that would contain all the meta data for whatever standardized scheme for informing multifactor/username/email api combinations you eventually come up with. Just because /.well-known/change-password exists it does not in any way limit what other suggestions can be made and implimented later (it only means that you need to use a different url).