We know you are patiently waiting for this feature. This feature is being implemented in stages. Fast tenant switching is currently in testing both internally and with early customers. We expect to release to the public in the Fall. I’ll post an update once it’s rolling out.
Full multi-tenant, multi-user support will be added after fast tenant switching.
~AlexChristian Haberl commented
It is a catastrophe for us, that after switching off Skype for Business, all my employees are not reacheable in our teams tenant anymore, when they are in a client's tenant. Fix this fast, or we will need another messaging solution.
This feature request is working its way through the backlog queue. No new details are available yet.