Former Bloombergian, now Villein, Alexandra Scaggs has written about this a couple times e.g. "Dollar surge pricing will be in effect through October".
It's kind of a big deal.
From Bloomberg:
Final wave of cash set to move from prime, muni funds
Shift seen before Oct. 14 compliance date for floating NAVs
With a seismic overhaul of the $2.6 trillion money-market industry
weeks away