I'd like this, although they'd probably limit the motifs we can get to ones available in the crown store (and probably not in the crown crates), and they'd have to be bound like the books. I'm also worried they'll make it so the total price ends up being more than the book would have been.

I'd be happy even they even just did it with the books. Where you have to purchase the book, and once you use it, you receive vouchers for any chapters you didn't earn. The only thing that might stink is that rather than a 1:1 exchange, there would have to be values assigned based on Crown Store cost, so that people can't "cheat" the system by using cheaper, more easily obtainable motifs to purchase more expensive motifs at a cheaper price (ex: learning all but one Assassin's League motif, purchasing it in the Crown Store, using it to get 13 vouchers, and spending them to buy 13 Ancient Orc motifs).