Is there any chance we'll see cards directly referencing characters/locations/events from The Hedge Knight novellas?  I would love to see Dunk and Egg cards!

I don't think we will, not that I wouldn't be happy to.

If they did make them though it would make a cool expansion box once they were done with all the houses.

*(very small) SPOILER from the Tales of Dunk and Egg *

I'm not so familiar with the CCG card pool so I can't speak to that.  In the LCG, there is a card for Daemon Blackfyre.  He does not really appear in the tales of Dunk and Egg, but his story figures fairly prominently into The Sworn Sword and as far as I recall he's not really mentioned in the main four books, so he's evidence that FFG is willing to tap into the Dunk and Egg source material.  My understanding is that FFG used to have a policy against printing things from before the start of AGoT, though they obviously have broken with that policy in a handful of cases since the switch to LCG.

The predominant speculation is that the licenses for the ASoIaF novels and the Hedge Knight "short" stories are probably different - and that FFG has card rights for the one, but not the other. FFG many not be contractually allowed to make HK-based cards without renegotiating the current license or purchasing a new one. And with so much still open and untapped within ASoIaF, they may not feel the need to do that.

Characters/locations/events that are part of general Westerosi history (like Daemon Blackfyre) mentioned in both story arcs are one thing - characters/locations/events specific to HK are another.