Tasks Quests Achievements
This is a pretty big one in my eyes, but an option to add users or to display the opposing players full tag when playing them is one suggestion.
My second suggestion was to add a lot more tasks or challenges to dailies and maybe instead of rerolling give the user the option to which they get to pick in order to complete. Some of these could also perhaps earn rare or mythic wildcards?
My 3rd suggestion is add more challenges to Sparky. Sometimes players are burnt out from the intense competetive scene and prefer a cpu opponent, but that offers little to no incentive.
My 4th suggestion is a page devoted to displaying a player's past rankings, and/or the updated stats they have.
My 5th and 6th final suggestions are to make multi-player modes that exceed 1v1, and to make Historic Brawl competetive.