I was talking about this in discord the other day.

What people are trying to do with stable coins is create a money market fund. But reinventing the wheel to do so.

What libra is doing is essentially the money market approach. Hold a basket of securities that targets a NAV of 1.00. If you hold a basket of 5B USD in cash, t-bills, and such, you'll make about 1% interest per year. So over the course of the year, you can issue 50M coins which represent the 50M USD in interest you are earning.

In reality, you'd issue something less than the full interest income so as to make the whole venture profitable.

This is also sort of what Tether was trying, but their transparency is zero and I wouldn't trust them as far as I can throw them.