It occurs to me that the easiest way to flush out the risk is for AV1 to launch a defamation case against any patent licensing pool which claims to hold a relevant patent. If it’s a lie, that is straight up defamation.
(Or a similar tort/breach. In Australia it would constitute a case of misleading or deceptive conduct under the ACL.)
This particular form of suit may be difficult in the U.S, owing to a somewhat different set of tradeoffs. It might be simple commercial fraud, if you could prove that they had misrepresented their certainty that their pool contained patents which they reasonably believed to be essential to implementing an AV1/VP9 encoder/decoder; though I think it may be very very hard to prove something like that.
And if it's not a lie, and they're going to find some judge in East Texas who'll see infer some infringement among one some detail in one of the bazillion patents in the pool, you're screwed.
Patent cases of this sort seem to broadly favour the litigant so why stir the hornet's nest.
It wouldn’t be a patent case, it would be a tort. Either you win and the problem goes away, or you lose and you know which patent you need to rewrite around.
For the cost of some legal fees, a loss seems like a great value.
(Or a similar tort/breach. In Australia it would constitute a case of misleading or deceptive conduct under the ACL.)