Some Jackpot chance is nice, but I think it's better to have that as a standalone for the other packs, as money has to be made as well.
Have them at the Jackpot-percantages of the reward chests could be okay, so it's one in 100.000 packs or something like that. Also, if you put in legendary, what about epics? The whole idea of these packs was to have them rare and common only, and I think it would be good to stick with that.
Though the micro-transaction-argument is interesting, it's also one of the things that have been critized most about games, since they're manipulative and stand for company greed. But that's a different discussion :-D