They really dropped the ball with that announcement. They didn't mention that volumes (therefore, services with volumes attached to them) are not yet available on Railway Metal.

Search this channel. there have been like 30 threads about this today

Volumes on Railway Metal are expected by end of March if all goes well. Also, this thread will be closed automatically unless you respond with N/A.

And, that eligibility for new pricing is not tied to the number of migrated services, but rather to the usage costs incurred.
If you have a very pricey service that you can migrate to Metal, you will become eligible for the reduced pricing after its fees contribute >80% of the total spend.

Again, they didn't word this correctly in the announcement. They used the word "80% of workloads", but meant "80% of fees must be incurred by services using Rainway Metal".