Short version: Can you reveal a Reaction Card you draw after being attacked by Soothsayer?
Long version: I encountered situation playing an IRL game yesterday, I would play a Soothsayer, my opponent would take his curse and draw his card, and would draw Horse Traders. He asked if he could then reveal the Horse Traders, and I wasn't sure. We went with not revealing the Horse Traders.
Thinking about it now, I don't see how you could reveal a reaction card. What if you draw Moat? It's not like it can prevent an attack, you've already taken your curse and you've already drawn a card; it's a bit of a Catch-22. Horse Traders is a situation though where if you can get away with this, you definitely want to for that +1 card next turn, so I said I would check.
I apologize if this has been asked and answered before, I looked through the forums a bit and couldn't find anything. I know for example that you reveal reaction cards you draw with a revealed Secret Chamber, but I think that's a different situation.