> If one DC becomes inaccessible does that count as an outage? It'll sure feel like it to the affected users, but the vast majority can still use your service.

Then put that on the dashboard! It certainly is an outage for the affected users (by your scenario).

   - 999/1000 Data centers up
   - 100,000 Users without service
   - 6 paying customers without service (will get money back)