Certainly a possibility. We've already seen deck requirements for specific cards, no reason why it couldn't be a class of card.
I do like freedom mixed with restrictions lol. I'm a weirdo and like my rpg classes to do the best by telling me explicitly to use this or this.
Incentive is probably more likely than requirement, like the investigator who draws cards for each tome (I forget exactly how it's worded). She doesn't have to play tomes, but she encourages it.
Actually, in a limited card pool, she actually might have to. But you know what I mean.
Yeah you'll probably be using all the tomes in Core set.