I didn't know that they were implementing that, My bad.
I don't know if someone has done this, but you could see how many packs you would need to open on average to get a complete collection. And maybe use that data to determine how much BFp you should get. For instance if you need to open 300 packs for a complete collection and people could earn enough BFp a day with daily quests and playtime to purchase 1 pack a day, that means that in about a year you've got a complete collection.
People like being rewarded, and getting a pack each day is a nice reward tbh. I personally think that you should be able to complete a deck (just the cards, not upgrading them) that you want in atleast a month.
It's a difficult thing to balance, but I'm sure the team will find the best solution. The quest system is a FANTASTIC idea and hopefully fills the gap that the paid transaction's left.