Enforcing 2 factor authentication without claiming domain

Problem Definition

Jira admins need to enforce 2-factor authentication but with many external partners with Jira and Confluence, and they will never be able to control their email domains, but would still like to enforce two factor to our Atlassian cloud instance.

Suggested Solution

Allow the possibility to use 2-factor authentication on all users (domains not claimed). 
Another solution could be to allow per instance multi factor authentication for the instance site admins