Impulse doesn't work like STEAM does. There are ZERO games on IMPULSE that lock itself to IMPULSE.
Any digital dnload you buy that IMPULSE has, but you bought it on STEAM or ORIGIN or D2D or other... There never will be a time where you have to register/install the game into IMPULSE just to play it.
The fact of the matter is that IMPULSE team and GAMESTOP are going to take the exact same approach as STARDOCK.
And that approach is to never force video gamers to have IMPULSE up and running just to play your purchased game.