Seamless Application Access and Lifecycle Management for Multi-tenant Azure AD Organizations

That sounds great indeed! And perfectly timely for us.

But I support AengusM comment on Teams experience: If we want a seamless experience, users should not have to switch tenant for collaboration. That's mostly achieved with B2B Direct connect, where externals can collaborate to teams shared channels from within their own tenant. That's proper cross tenant collaboration. 

But, what about chatting..? When Nestor from Contoso US will start searching "John D" for John Doe in Contoso EMEA, Teams will suggest the John Doe's guest account on Contoso US tenant, not the external one from Contoso EMEA (Nestor would have to type the complete email address for that). Chatting with the external Contoso EMEA is however the perfect experience, John Doe can chat without switching tenant.

I think Teams collaboration with guest account should be avoided at all cost ; it forces users to switch tenant which is a terrible experience.

Do you plan to address this issue? Maybe by listing externals account behind B2B Direct Connect at the same level as Guest (or even before).