It's a hybrid of the business plans of Ting (variable month-to-month pricing without penalties), T-Mobile (free international texts and data), and Apple (special SIM card).
Not to mention Republic Wireless. In fact, a few days ago, Republic Wireless announced that they intended to start testing a cell phone plan that pays you back for data you don’t use. The concept renderings show that they might give you control over which processes are allowed to use cell data.
In the meanwhile, Republic Wireless already has WiFi to cell handover, and $25/month (before taxes) gives unlimited minutes and texts and data at 3G speeds. That’s only 500MB on Google’s plan. $40/month gets unlimited 4G on Republic Wireless, but only 2GB on Google Fi. I’m not especially tempted by Google.
The downsides of Republic Wireless are that it’s Sprint-only, you have to buy a Republic Wireless phone with a Republic Wireless firmware that is several months behind Google and Motorola’s firmware releases, handover is not actually seamless in my experience, and there’s practically no roaming. I’m willing to overlook a lot, though, because I’m personally on the $10/month (before taxes) no-data plan. That’s half of Google Fi before data.