Pretty tough to do statistically right? Not a real threat from my view..
Discussion
I remember reading a paper from like 2013 explaining why it wasnt a big deal but cant remember more than that
Selfish mining is risky to attempt. Sometimes you win big. What I am worried about is collusion with selfish mining (which is basically 2 pools added together being more than 50%) (like foundry and antpool) which can frequently win selfish mining attacks. They would get caught pretty quickly and it would be an industry scandal and tank the price for a bit. But it would definitely shatter mining pools into tiny bits.
Sounds hype
Sometimes collusion may be involved. Right now Foundry + antpool is just over 50% of network. So on paper they are separate pools, but who knows if there's communication.
They're just pools, not miners. Miners are the ones who would be colluding or communicating. And I wouldn't be surprised if there are some large miners who mine on different pools at the same time, just to avoid the pool getting close to 51%