This sounds a bit misguided. IIUC, Google Fi is really a mechanism of accessing two carriers from the same device. It consists of 1. A partnership between Google Fi (the cellular provider), T Mobile, and Sprint, and 2. A special radio hardware on the phone that is capable of working with two different "channels" at the same time. Since my Nexus device broke, I have personally been using "Google Fi" (the provider) on my iPhone which means I do NOT reap the full benefits of Fi without having the special radio hardware.

So, I don't think it is physically possible to do the "two provider at the same time" thingy without a special hardware (you'd need two parallel "radio" circuits on your phone).

And with that, your analogy falls sadly on its face, as you seem to indicate an artificial "software" limitation has been set to prevent us from using Google Fi on our iPhones.