Two things I'd enjoy if they were added to the game
Love this game and how accessible it is to play a wide range of decks without spending nearly as much money to do so, even free is even an option, which is great.
There's two things that I would enjoy if they were in the game, both would be nice but I'd be happy with one if the other is too much to ask.
Sparky difficulty levels - Sparky is great to test if your deck has the right amount of lands or mana generation, but it gets repetitive seeing the same basic decks from each color. Adding difficulty levels to Sparky by giving her/it decks that have a wider range of archetypes like Landfall decks, Milling, Control, Combo, etc. But if that requires a lot of AI programming, my other idea would be easier to implement.
Self Battles - Just like it sounds. Pick two of your own decks and play both sides of the battle. It would be a good way to practice your replies to specific deck archytypes and test out your new decks against more nuanced decks than Sparky can provide.
No reward for playing either of these game types, obviously. Just more options for practice.