I'm always iffy about concepts that attempt to let the player invisibly set what card it summons. Things like this become impossible to effectively balance. There's at least one older concept that does something similar but summons the first card in that rarity level in the deck, and we had similar discussion then.
Also, what happens in case of a tie? And how unfair is it for a site update to change the functionality in a specific deck in a game in progress? Cards like this can be a real pain...