Prediction: Second Dinner is preparing to announce that some cards will be forever pool 4. It solves both the meta game issue and the hoarding issue without making players feel bad about their cards getting downgraded.

It solves the meta game issue because Second Dinner is in a unique position where they have to manage multiple meta games depending on your collection level. Locking game changing cards behind pool 4 for pool 3 incomplete players reduces the probability of losing control of the meta game, thus preventing one sided matches that result in people quitting the game.

It solves the hoarding issue because it gives pool 3 complete players something to spend their tokens on without worrying about choosing the wrong card.

It opens up the long term possibility of a pool 6 once there are enough cards in pool 4 to make it a stable tier with it's own meta game. They can't remove cards like Hearthstone can, so this is really the only path forward for them. Remember the feeling between pool 1 and 2? In a few years Second Dinner hopes to extend that feeling to pool 4 and beyond, and maybe expediting the process for future newcomers.

It gives pool 3 and big bad complete players a reason to come back to the shop for forever pool 4 cards.

So far it looks like Darkhawk, Knull, and Zabu will be forever pool 4.