I agree. It's a very interesting idea, but would it be a dead card on a board without trash-for-benefit cards? There aren't really that many -- Salvager, Apprentice, and Bishop are the main ones. Self-trash-for-benefit would combo nicely, too: Feast, Treasure Map, Horn of Plenty, Embargo. With trash-as-side-effect cards (e.g., Trade Route), you'd have a small chance of being able to play them safely more often, but it probably wouldn't be worth eating up a card slot on that off-chance. It would be a good defense against Pirate Ship and Saboteur (but possibly not Thief, depending on how you rules-lawyer its "gain these trashed cards" clause).
An awful lot of boards have none of these cards.
But you might be able to make it more universally useful if you can get it to give you a benefit no matter what card is trashed. For instance, if, when you Chapel away a Curse, you could reveal Cupbearer and gain some additional benefit -- while still having the Curse trashed -- then the reaction effect might not be so specialized in scope as to be usually useless.
Maybe something like:
"When you trash a card, you may reveal this card from your hand. If you do, you may choose one: place the trashed card in your discard pile; or, +2 Cards and discard this card."