It would be awesome if you could have multiple bot difficulty settings so that way you're able to give your decks an actual test before trying them against people. Plus giving the bots better deck selection of course.
It would also be sweet to be able to watch a friend's game. Just from your friend's perspective that way there's no cheating going on.
Brawl would probably be more popular if you gave it ranked matches, same with the other modes. Also would be cool to have Archenemy and planeschase as match options
Lastly I feel like the Vault wildcards would be a lot better if it gave you more than 1 mythic, 2 rare, and 3 uncommon. You have to get a ton of cards to finally open the Vault and it only has a few wildcards. Maybe make it give like 3 mythic and 5 rare, and no uncommon. Or perhaps just 3400 gems instead of wildcards