Plausible, yet miners choosing to introduce something like OP_ROUTE would so knowing that the USD value of Bitcoin would most likely plummet. What's in it for them? Why destroy the whole thing and get left with a bunch of useless equipment?

This assumes something of a free market when it comes to exchanges, which is not the case. They are market setters. They are not takers and makers. The entirety of Wall Street is completely price-fixed and Bitcoin's USD price is no different. But as I wrote, this would be a slow, increasing process, boiling the frogs before they realize they're endangered, they're already trapped in this vicious cycle. It will be pushed as we have to fund the "security budget." We have to make sure miners stay profitable. Plus, people don't realize that if they don't push a URSF, then it wouldn't matter anyway what their nodes say.