For the Yssaril does cultural crisis cancel their ability to have more than 7 cards in their hand? Does cultural crisis force an immediate discard of the surplus?

Yes. It's just like if something external happens to suddenly cause you to exceed your fleet supply - you have to remove ships to comply. The same thing applies here - if you don't have the "ability" to store more than 7 cards, you must immediately discard down to 7.

Always a good card to hit the Yssaril with in the late game when they have over 10 or 15 cards and see the player scamble to keep the best ones if his Agents are already gone and he then tries to either play a Sabotage or buy one off another player. I have had a hand full of over 15 cards before and not one Sabotage.