Don't you realize the irrationality of your statement? You buy the Spell-book and then afterwards optionally some packs. That's already the way it is done right now. So it doesn't make sense to add this feature optionally. No, my proposal is radical: destroy the NULL option.
If this is a problem for you, then you are totally wrong at Splinterlands. Maybe try Heartstone. Ooooops. You also have to buy packs there too? Oh no, is there any card game I don't have to buy packs? Magic the Gathering maybe? What community are we growing here?
I guess I'm wrong at Splinterlands 🤷♂ Glad to see your proposal is doing so well