If anything, this moves it towards anyone having more access to everything. For example, reject isn't going to be treated anymore as a bounce. Now, provider policies still can and would be BS, but the standard doesn't tell them to do it certain way.
User numbers aren't the only factor. Microsoft has a much larger presence in commercial email than Apple. I suspect an outbound email from a personal provider is far more likely to be destined for an outlook inbox than one on iCloud.