Our corporation also requires this as we are sharing our connections with customers between our users. Many of our customers require that two factor authentication is enabled for unatended access to their machines and per now I can't find a way to check what users has this enabled and to enforce that they keep this activated.
Please incorporate this feature as soon as possible!
if I can try to make a suggestion: try to implement a federated authentication mechanism. This should allow you to keep the authentication mechanism private (both on-premise via ADFS or on AZURE AD - AAD). Here you will find the technical documentation for the activation of the mechanism necessary for the federation.
Once you have activated your identity provider to access the TV client, you will be able to manage the MFA (Multi Factor Authentication) in the most convenient version: telephone call, SMS, etc.
Credentials check, MFA, lock user (dismissed employees), change-reset-remember password and so on. And finally SSO (real Single Sign On)
I believe that it is highly difficult for TeamViewer to meet all the needs of control of the most structured customers and the choice to delegate authentication to external providers is the one that is more in line with the future GDPR.
Hope this help.