It is not clear to me why schools such as Harvard, Penn and Stanford that have had consistent and typically high yields in the past would "massively-underaccept". I get that they may have underaccepted somewhat this year, but massively so? Sure, they're operating with imperfect information, and the information is incomplete, but they know from past experience typical yields (which is unlikely, in the end, to change this year, despite the new traffic rules), they know the many students who have already CTE'd and they know only a small percentage of those who have PTE'd are likely to get in off waitlists. So I suspect it is a bit less problematic for the high yield schools.
But If what gyngyn say is true, there will be major movement very late in the cycle when schools bump up against their CTE deadlines. Chaos will then truly reign.