They either need to pare down the list (eliminating the chaff) or put a list card in EVERY set booster. Their stinginess is far beyond welcome.
As far as we can tell, the frequency of these cards will be seperate from The List's size. If they're guarenteeing one in every 8 set boosters, they'd have to be either 50% of The List (unlikely), or they're effectively a seperate "slot" from the normal The List. The latter seems far more likely to me. So the main question mark to me is whether they'll be supplating "normal" pulls, meaning that the frequency of other The List cards will go down to 1/8 (to make it 1/4 packs having "The List" cards in them), or if they'll be supplemental. Either way, there should be plenty in circulation.