Some ideas I've been playing with, based on a theme that will quickly become obvious. The appearance of Poacher inspired me to finally post them since they work on a similar basis. Very, very untested - in particular the prices here are basically just guesses so I'm sure there's plenty of balance issues. But please let me know if you think these would work ok, and if the theme is worth exploring.
First, some symbols:
{X} when X is a number means "there are X empty supply piles"
{X+} means "there are X or more empty supply piles"
{*} means "the number of empty supply piles"
BURNING VILLAGE (2)
Action
+2 Actions
If {0}, +1 Card
RANSACK (3)
Action
If {0}, gain an Estate
If {1}, gain a Duchy
If {2+}, gain a Province
RIOT (3)
Action/Reaction
+1 Card
+1 Action
If {1}, +1 Card, +$1, +1 Buy
When you trash this, +2 Cards.
DEAL (3)
Action
+$1
+1 Action
+1 Buy
If you've already bought a Deal this turn, this costs £1.
GRAVEYARD (3)
Victory
Worth {*} VP
CRAZE (4)
Treasure
If {0}, worth $3
If {1+}, worth $1
DOOMSAYER (4)
Action
+1 Card
+1 Action
If {0}, gain a Silver
If {1+}, gain a Gold
FORTIFY (4)
Action
+$2
+1 Buy
You may place this card on a supply pile, empty or otherwise, to fortify it. A fortified pile does not count as empty and no more cards can be bought from it until a player "buys" the Fortify card for $5, trashing it.
SANCTUARY (4)
Victory
Worth 1VP
When this pile runs out, the game ends.
PROFITEER (4)
Action
+2 Actions
+2 Buys
While this is in play, if a pile empties, +$5 and +1 Buy.
COMET (5)
Action/Attack
Each other player gains a Curse.
If the Curse pile is empty, +$3.
At present it definitely needs a good trasher and a way of returning cards to the supply - I haven't settled on designs for these. Some pile-emptying gimmicks a la Talisman/Port/Salt the Earth would be good too, and split piles would be a nice fit. Not sure if Sanctuary runs afoul of the "strictly better" rule?