I love this idea. It could be implemented relatively painlessly for Zanz, and would make the game a helluva lot more fun. Ideas:
NOTE: Numbers are just approximations, the idea's the important thing.
-Elements tracks how many wins you have for each realm. When you accumulate ten in all four realms, you win a random upgraded rare chosen from the realm of your choice, after which the tally resets (it doesn't matter how many wins you rack up in one realm, only that it's 10+). This will encourage people to fight in all the realms, and make people that just focus on one and get a slightly higher win rate overall miss out.
-Once you accumulate 50 (or 100, or more) wins in all four realms, you get to face a random false god. If you beat him/her, you win a superspecialultramegasecret high-cost, high-power rare. Each time you face this special false god (randomly chosen from all of them) and win, the game records this, and you will never face that god again in this manner. Once you defeat all of them (you'd have to rack up 4800 wins in total, plus extra if you don't get to exactly 50 or 100 or whatever the quota is in each realm at a time), you get some bonus/prize, such as being allowed to fight false gods for free, or getting a 33% extra chance to spin the slots a bonus time every time you win, etc.
-Once you defeat all of the false gods in a particular realm a certain amount of times (~10), you unlock a new false god in that realm which will pop up a small percentage of the time (~5%) and will be super-hard but also carry a much higher reward (bonus electrum, spins, guaranteed cards, that sort of thing) if you win. He'll be much more difficult (draw 3 cards per turn, start with cards on the field, must be defeated twice in a row to be truly defeated, the second time starting with 100 HP, etc.) but defeating all of these bosses unlocks a super-ultra-difficult super-boss, or something like that.
Anyway, those were my ideas on the subject, clearly some of them better than others (lol), I'll close by saying I really love the idea, think it will make the game much more fun (not to mention bearable - I can't farm for more than an hour before getting sick of the monotony of having no idea if I'll win just because my deck is built to have as high an overall-winning-percentage as possible, and so isn't particularly good against almost any one false god) for everyone, and am keeping my fingers crossed.