Project Fi has made a small, but important, change to the way it operates, opening up the service to those who use paid G Suite accounts rather than just consumer-grade Google accounts. Now businesses or families who have opted to pay for G Suite accounts and use a custom domain can get in on Project Fi rather than create a second account just for their Fi service.
Now this still creates a hassle if you chose to use Fi on a secondary account to start and now have to switch it over, but going forward this is at least one more restriction dropped in a long list of issues where G Suite isn't up to speed with the capabilities of a free Google account. Combine the new G Suite compatibility with Project Fi's group plans, and you could see this being a good option for people who want to use Project Fi for a business phone line.
If you're not the administrator of your G Suite account, you'll need to have the admin turn on Project Fi access manually — it isn't turned on by default.