wroot The M365 Admin Center see's 1/3rd of its traffic from partner and larger organizations that manage multiple tenants. This is an experience catered to all or them (Partner and enterprise) so they can do the things you would normally do in the Microsoft 365 admin center more efficiently across tenants. The M365 Lighthouse experience that is in development is a specialist workspace for Partners specifically.
MartinDay One of the way I usually explain the efficiency gains from this is thinking of the Service Health information. Lets say you manage 15 tenants, you would have to log into each of them independently and see which service incidents are effecting each tenant. Now you can get that information in one place. Happy to take feedback on the experience though, especially as you use the experience on if you still feel like you are making mistakes on which tenant you are managing, we actually went through a LOT of research to try to get that right.
wilhil The tenant switching experience is something that was built to be reusable by other Admin Centers, as an example at Ignite Exchange Admin Center announced they are integrating it soon (I am not 100% sure on the date). As for the limitation of the delegated admin accounts for partners, I cannot make an announcement, but I can confirm we are working to solve that.
Coen Verbree Azure B2B support is in the final stages of development and we hope to have support for that very soon, but I prefer to not promise a date till we validate the experience. Our target is before the end of the calendar year.