I have never seen one that would work in the wild. I don't think it is possible. We've had plenty of time to see something somewhere, but nothing. I gone through the papers, read other code, I've seen nothing that didn't require help from the target.

I don't accept the general hand waving "they keep getting better" because they haven't.

Most of these the exfiltration rate is so slow that simply xor'ing the secret with a random seed that changes locations or moving the memory around itself would prevent any attack.