Back in the good ol' bad days, P+K was i13 and -8 on block. I don't think I was ever thrown after block. -8 is unsafe, but it's a small enough window to allow lag to make it safe. Trying to punish it with an -7 throw was likely to fail, so you'd have to be super quick about doing a neutral throw instead, which is breakable. But really, the entirety of the animation is so fast that I think most people simply couldn't react to it quick enough.
Nowadays, it's i10 and -12 on block. That's a pretty huge buff in speed and a pretty big nerf in safety. Nevertheless, I still rarely see this punished. Again, I believe that the animation as a whole is just too fast for a lot of people to realize they can punish it in time.
I even had cases where an opponent did it twice in a match after performing the first one on block and then immediately doing it again beating out an i13 mid, which isn't exactly possible due to the added negatives from performing it on block in the first place.
Yup. This worked back in the day way more often than it should have simply because people were usually too slow to react to it. It wasn't super rare for me to throw out P+K again immediately after having it blocked and still score a hit. This should still work with Nyo too because even though she gained 4 frames of recovery, it's still a very fast animation overall. Not that I necessarily promote the idea of attacking from disadvantage, but if you want to mess with this for shits and giggles, you'll probably score more counter hits for being dumb than you'd think.