The biggest barrier for anyone wanting to try and use stadia is internet speed and not data caps or distance to the data centres. If you connection is too slow you won’t be able to use Stadia. Stadia can be used at various speeds from 10 Mps for 720p and 35 Mps for 4k 60fps action.
Stadia has included a speed tester to make sure you use Stadia. This will tell you if you meet requirements to use Stadia and it will also tell you at what quality you can play at.