I was wondering what happens with Satin and an opponent that has reached his draw cap ... someone suggested I could not even trigger that option

Reveal the top card of each player then choose one - each player returns to deck, discards or draws the card

So I trigger this and select Draw - one player has reached his draw cap.

Assuming I can do this, what would they do with the card?

This is one of a few instances where we are not sure what happens to the card

Another was triggering Gates of Winterfell and the revealed card being an unique that is already in my dead pile ... what do I do?

Reveal the top card of your deck. If that card is a Stark character put it into play knelt. Otherwise discard it

Gates of Winterfell is no mystery. If the card can't go into play, you discard it. The "otherwise" covers all situations in which the "put into play" effect does not apply.

For Satin, there is no part of the effect saying to discard if the effect cannot be applied to the card - so it stays where it is (on the top of the opponents deck). Choosing which effect to apply isn't like choosing a target, so you can choose an effect that will only be partially successful (ie, not everyone can draw).

1) If the opponent cannot draw the card, they return it to the top of the deck. This is because the revealed card is still the top card of the deck.

2) Same thing as the Satin scenario. If you cannot put the revealed card into play (due to being unique and in the dead pile), it stays on top of your deck unless otherwise stated. In this case, it tells you to discard it if you cannot put it into play.

Thanks - for Winterfell I was reading the "otherwise" as being whether it was a Stark character, not whether it was possible to then put it into play