Hearthpwn

Firstly everything I'm going to say is going to assume heroic.  It's been declared that normal is meant to be interesting and easy so that it's not a barrier to getting the cards.  Normal mode is not meant to test or prove yourself worthy: instead it's just a way to deliver the cards to you.  Ok that said:

That's not easy really.  From what I've seen of CCG AI, you aren't really going to get too much into the way Normal players operate.  As such the best I've seen AI systems do is to present a puzzle that doesn't work on normal decks.  The idea is that you are meant to look at the rules and cards played and determine the deck setup required to beat the puzzle and thus the match.  I've seen some setups where, for example, The opponent healed 30 every turn and had a ton of board clears, thus making mill the only way to win, heros that wil literally destroy any minoin that didn't have a specific mana cost, heros with lots of burn and an ability to kill you if you went below 20 health, and one crazy one that damaged you for every card you drew, played, or lost.  Once you knew the deck the matches were easy, so the point was to NOT look them up and deal with the challenge on your own.

the question is whether the populous really would care for something like that.  WE may but we're .001% of the population and NOT influential, so it is up to the question whether the extra benefit some will get from the challenge will overwhelm the ones that get frustrated over a hard design or disappointed since it's 'puzzle' based and not some possible-only-in-dreams epic battle that makes starcraft look like shoots and ladders.