Two things:

Any word on implementing an achievements system in Hearthstone?

Probably a fairly simple feature that would go a long way to increasing the playability of Hearthstone.

Being able to earn single cards from older expansions?

With this many sets now, any newer player is going to have no hope catching up and playing old cards like Yogg, Ragnaros that you devs often reminisce about, without spending extra money on cards that all us older players earned for free.

You could tie in the old rewards we got like a free C’thun and Marin to the achievements system, why would a new player want to spend money on Wild packs if they weren’t already enjoying the game, but are missing so many cards for Wild that it’s unfeasible for them to craft every card with dust? Say all the staple cards of old like Piloted Shredder, Coldlight Oracle, Dirty Rat.

If you want an example, Eternal card game does this better: you can earn cards from the sets you missed over time because you’ll get a card here and there from their various draft modes, and also packs, even though they do focus on more packs from the latest expansion. In Hearthstone, you only have arena offering the latest expansion packs, with the odd card here and there of Standard only but it’s a rare occurance.