I only watched a very short part of that video but I don’t really understand the point.
Assuming the “toxic waste” was kept it would theoretically enable the generation of false proofs. However from my understanding that’s not going to enable developers to “see what’s going on” as notes (Zcash equivalent to Bitcoin’s UTXOs) are then encrypted to a user’s transmission key before being stored on the blockchain. So, I don’t see how knowledge of the “toxic waste” enables anything other than being able to generate additional ZEC in the shielded pool and it wouldn’t enable auditing.
Already it is possible to monitor amounts coming into and out of the shielded pool (so it would be possible to detect an inflated money supply that way) and also a turnstile type audit will happen for Sapling when moving between the Sprout and Sapling circuits see https://github.com/zcash/zcash/issues/2248. Basically, in moving between circuits the amounts will be revealed such that the total number of ZEC moving between the shielded pools can be monitored.