Here are two features that to me are very important for competitive players.
1) Better way to know what is in your deck.
I already have a problem with summoner wars having to track every magic pile and discard pile to know what´s left in your deck. But that is on 1 on 1 game. When you are playing 12 games at the same time, something not uncommon for me. i often get lost on what´s left on my deck, specially because i can´t check my opponent magic pile. Maybe there are walls, commons or even champions, that i should know are there, and yet i do not because i don't remember in 12 different games. A similar thing happened in a Bender vs Phoenix elves where i forgot my opponent stole a Burn and i paid for that greatly.
So a good way to solve that would be to a) being able to see what´s left in the deck being able to see what opponent magic pile cards we ¨know¨ as well as hand. c) give a ¨step back option¨ so we can review past turns.
2) Replays would be so good, so hard to talk about game analyse strategy or talk with others without having handy replays.