SA's use the X button like Boarding?

If the Spartan Abilities are situational like boarding a vehicle or dual- wielding, and use the X button in my case, and there are no AA’s what is going to take the AA’s button? Also if they remove sprint as many of you believe isn’t that 2 buttons that need something? What could go in these open spots?

> If the Spartan Abilities are situational like boarding a vehicle or dual- wielding, and use the X button in my case, and there are no AA’s what is going to take the AA’s button? Also if they remove sprint as many of you believe isn’t that 2 buttons that need something? What could go in these open spots?

In Halo 3, the grenade switching button was by default LB instead of Left on the Dpad (Which is a nuisance to reach) and so was dual wielding, it is possible the SAs use a different button to not run in the way of other activities (ever tried picking up a weapon while near a vehicle?).