Like the strong financial incentives to compromise certificates owned by banking websites? Securing voice communications the same as website communications is an awesome idea, and the fact that it’s possible to steal some piece of data and compromise it shouldn’t prevent us from moving in that direction.
It has happened, but there has to be a big pay off to make it worthwhile.
Smaller companies would likely be more frequent targets given they would be easier to compromise.
By the way, I'm not suggesting that the idea is useless. I'm just pointing out it isn't a panacea, and it still doesn't address the core problem raised in the article that you don't know if you are speaking to a human or not.
But the point is that the pay off itself is limited. Smaller companies have a much smaller pool of people who would have any reason to accept unsolicited calls.
This is evident in how scams work today: you either get explicitly targeted, or you dragnet using some service which everyone has i.e. a bank, the tax office, or a telecom company.
Compromising "Joe's BBQ Emporium" might be easier, but it's still (1) something you have to do (and maybe get caught then) and (2) the number of people who are going to pick up, or not immediately blacklist unsolicited calls from "Joe's BBQ Emporium" is tiny.
Does it matter if you’re talking to a human or an AI? The main thing is its intent - is it helpful, or malicious? And attaching communications to persistent reputations via certs can help guess at that.
And you still don't know if your taking to a human or an AI.