So, in other words you need a Cyrus's Conspiracy and an Unown Q in your hand and a Garchomp on the bench which was there at the start of your turn. That's not much of a stretch.
If they have a viable target on the bench to snipe already, it still plays as good strategy to fill their bench with Pokemon that can't evolve and have coming in to play powers (pixies) to keep them from benching other more important Pokemon or benching a pixie from their hand and getting to use the Power. Then you can just snipe it at your leisure...
Isn't it a stretch? In a deck with little draw or search for non-basics, I find myself expending a lot of energy to get Honchkrow itself, let alone Poke Turn and Unown Q.
They can still bench a Pixie, if you just took a prize. Plus, late enough in the game that there would be suitable targets for Darkness Restore, your opponent probably has BTS in play and/or a full bench and/or control over their discard pile.
90% of the matchups where you want Honchkrow are against BTS heavy decks. Donphan, Machamp, Gyarados. The only exception I can think of is Dialgachomp, and again, it takes 2 turns to charge Honchkrow, especially where your opponent can spray a Galactic Switch.
Most decks against whom Darkness Restoring is a viable option are Stage 1/Stage 2 decks that run BTS. Darkness Restoring does not work against SP decks because of Honchkrow sniping options (Dragon Rush and Bright Look), Power Spray, and the fact that you usually have limited desire to snipe useless Pokemon when there are better targets in play.
And if Honchkrow is really the big "surprise" people boast it is, Stage 1 and 2 deck players will not have the foresight to withhold BTS.
Surprises don't work in Top Cut people.