Indeed, it can lock games, and it would even if you barred some cards (keeping only cards up to $6, or non-Victory cards) ; I think you should at least discard your own card when he reveals the named card (if you choose to make him trash) ;
What about :
Fearmonger
Action attack, cost $4
+$2
Name a card costing up to $6. Each player may discard a copy of it ; you do so last.
If you discarded, every opponent with at least 5 cards in hand who didn't trashes a copy of it from his hand or reveals his hand if he can't.
It may still be boring but the fact you've purchase power instead of +action makes it better. The problem is if you play two of them, you can gain information from the first one and discard/trash his hand this way so I added the italic part... it's heavy worded but easily understandable when you read it once, right ?
EDIT : oops, I forgot to add a restriction.
RE-EDIT : well, no, they would just discard their Provinces and Colonies anyway, lol ! But still, the $6 restriction for platina and KC ?