Problem: Libraries currently build up excess cards (over 4) a player will never have any use for.

I have been play-testing the game on Android and I can't easily tell when I have more than the playable 4 of a certain card. I have read that MTG has pushed back against a dust system as employed by other wildly successful digital CCGs, but Arena needs something similar to keep people from bleeding off to other games where their money is better spread across assets by allowing more flexible deck building.

Perhaps there could be a plane-melding or mana-melding of cards, where users can take two cards to meld, and receive a random card they don't yet own (or own four of) in return. This could be emphasized with mana color, or card-type.

Regardless of the solution, one is needed. The current system has a wasteful feel where players feel like they can't get the full value out of their collection. Drawing a new card you already have four copies of instantly makes you less likely to enjoy opening more packs. Giving those excess cards a user-controlled purpose puts MTGA back on pace with other lead digital CCGs.