This might already have been covered, but these are the features I think will resonate best with the Dominion demographic:
1. In-depth player statistics aggregate. I wanna see how much I suck with Tactician, or how much I overestimate my 5/2-skills on Mountebank-boards. Winrates, game length, buy-frequency - you name it! As mentioned earlier in this thread, ingame access to such a stats profile would be really neat. On a strategically ambiguous board, it would be fun to know your opponent's buying tendencies. Meta-strats.
2. A rating system that inspires improvement. I want a badge showcasing how much I suck, and complementary extravagant badges glorifying the very best of the best. The underlying MMR doesnt have to be hidden, but simply supplemented by something flashier than a 4-digit number. Starcraft does this in a semi-decent fashion, disabling mid-season demotions. In this sense, everybody gets the illusion of progressing throughout the season (a la Hearthstone).
These features might be mostly cosmetic, but their importance for game enjoyment is of great significance IMO.