The team is working on #2 (and has been for awhile). We will update as soon as we have more news.
Federation like S4B is a must in order to be able to fully replace Skype for Teams. Guest access is not really an option. In the case of Skype it's easy because each Skype deployment has its own Edge Server which serves as Federation Proxy. The simplified Teams architecture does not have this component, so something along these lines would have to be "created" or some other mechanism within each individual domain within Teams to act as a Proxy. It is not trivial... That said... it is necessary