I want to say that leaderboards are planned, but I don’t actually know that. However, stats definitely are planned. Levels technically will be added, but not as a general thing but more as a per-minigame thing. They’ll be called badges, and the next update will contain a button for them (though they aren’t ready yet, it’s just pre-planning the layout for when they are implemented).
Quests/Challenges have been discussed before and opinions have been fairly mixed, but the general feeling is that it would be better to leave them out (the game is about doing what you want to do, not what the game arbitrarily wants you to do).
The idea of getting a higher unit bonus for higher levels is interesting, but I don’t think it’s a good idea. It rewards playing the same thing over and over, and TU is about having a bunch of equally viable options.Besides, being good at a particular game will already give you more units than most others because you will tend to perform better. A few rewards for achieving certain milestones is fine, but more permanent bonuses should probably be left out.