I believe this is something the team are considering but theres no final yes or no answer.
It really isn't difficult to get games onto Steam anymore, not like it used to be.
There are pros and cons to Steam but usually its largely beneficial.
Theres also the question of making sure an account bought on Steam also links with the site accounts (seeing as most of us have bought the game via these packages). Also the question of whether we will need to buy the game over again to be able to use it directly on Steam, or will Grummz try to do what some other games have done where they sort out free steam keys for the backing tiers...
Its something we likely won't know until closer to launch, and its also not much of a priority compared to other things.