It's not much fun to split up a wireless family plan, especially if you're not splitting it evenly. How much do your kids owe if they're only paying some of their bill? What about that roommate who always uses too much data and drives the bill higher? Google wants to fix that. It's adding a Group Repay feature to Project Fi that lets group plan owners not only determine who owes what, but collect on that share in short order. You set the criteria for what members owe, such as a fixed amount or extra data use. After that, fellow Fi members just have to wait for reminders before they contribute their share.
When it comes time to pay up, you can use Google Wallet to both send and receive funds. If you're the plan manager, you can set up automatic transfers so that any repayments go directly to your bank account.
The feature is available in the billing section of your Fi account. It probably won't convince you to switch to Fi by itself, since there are still plenty of other hurdles (needing everyone to use compatible phones, for a start). However, it could be a tipping point if you were already thinking of signing up, whether you're starting from scratch or joining someone else's plan. Instead of breaking out the calculator every month, you could let Google do the hard work and spend more time actually using your service.