Announcing Public Preview of Inbound SMTP DANE with DNSSEC for Exchange Online

I think the documentation assumes that the example-com.mail.protection.outlook.com

MX has a priority of 0, and that the new MX will initially be added with a lower priority. You then recommend testing that mail is capable of flowing to both endpoints before making the new endpoint the default. It is possible that the old MX has a value greater than 20, and in that scenario the user is making the new endpoints primary earlier than expected. 

The documentation also assumes that people have not configured a "backup" MX record. It might be enough to say in the documentation "if you have more than one MX record contact your administrator for guidance", rather than trying to account for every possible complication of MX records.

At several points you mention the need to set the MTA-STS policy to "test". You should also mention the need to update the _mta-sts TXT record every time the policy is updated. If the "id" in the TXT record is not updated Sending MTAs might not check the policy at all until the max_age has expired.