Hearthstone has been slowly weakening the classic cards (equality 2 Mana nerf) this pushes the player into going to sets that cycle out. I think it makes it more difficult for new or returning players though, so their base will decline.
In contrast, with a game like MTG, even banned cards can still retain a decent amount their value to collectors and casual players. You get what you pay for and it's yours forever to do with as you'd like. Why pay tons of money for ever-changing pieces of digital paper you don't even actually own?
Balance would be tough (9 classes vs. 5 colors in MtG) but Blizz could do it.