See, here's what I see as the problem: you're taking an item because it's interesting and has a magic card--but if we look at it in gameplay terms, you've pulled a unique magical artefact with an [i]insane[/i] mana cost out of your ass. I'm not saying that Sorin [i]wouldn't[/i] have that sort of thing around--but the buildup given to 'suddenly, one of the most expensive and generic (mana-wise) cards available' is totally unworthy of the effect.

In roleplay terms, you're arguing that the categories for M:tG effects be broadened so that, essentially, [i]any[/i] effect requiring a creature or player can be fulfilled by literally any opponent. Rather broken, since it makes the actual target of cards irrelevant. You might be playing an experienced planeswalker, but producing any Black, White, or Colourless card that might be relevant on a whim gives you... what, 4,500 cards?

And on top of that, wanting to summon this demon is [i]astonishingly[/i] bad. From what it is and what it does, it would seem more of a threat than the dragon--plus it's intelligent and inherently malevolent. All that releasing the binding would do in the long term is [i]get Sorin killed[/i].