The prospect of having to pay for many Azure AD Premium P1 licenses just because you use an org-wide team is horrible to contemplate. But don’t worry. You don’t have to because the Teams developers look after membership updates for you.
The latest version of Teams supports the ability to create org-wide teams, but only if your tenant has fewer than 1,000 accounts. It’s a neat idea, if you can use it, but if you have more than 1,000 accounts, there are other ways to foster company-wide communications.