Agree, that's the challenge, an abstraction where you maintain the flexibility without the deprioritization. I admit, it may be impossible due to the inherant limitations of the model. With that said, from your link, Google Fi gets a high priority designation on T-Mobile ("QCI 6 goes to all branded plans, both postpaid and prepaid, besides those with Essentials in the name. Google Fi has QCI 6 as well."), so perhaps it's possible.