There are many Email Service Providers (hosted service) are looking for multi-factor or password less authentication using Oauth2. However Thunderbird OAuth2 is limited to few known OAuth2 providers like Gmail or Outlook. There is lot of demand for security feature (MFA) due to increasing fishing attack and loosing customers to bigs sharks like Gmail and Outlook.
As I understand TB is promoting K9-Thunferbird for Android and iOS will be there soon. If you like end users to adopt open source clients I feel OAuth2 support must without which there is no competition with Gmail or Outlook.