It's here, the moment we've all been waiting for, Defender for Business is live in tenants using the Microsoft Business Premium license aimed for sub 300 users.
The overview page here says the service is rolling out to tenants from 1st March and I can confirm it's available in my tenant and those that we manage.
While this is just a news update I am super happy to be putting out, watch this space for technical blog posts detailing how to deploy and manage the service!