Please put a temporary rail around that hole. I have seen too many horrific injuries caused by open holes like that. Nothing fancy, a couple of 2x4s screwed to the band joists as posts, and a top rail of 2x4. Or, screw a sheet of 3/4" plywood over the hole.
If you are going to sub out the sheetrock, set it up so that there are no joints anywhere near the new beam. Ideally there would be a full sheet running parallel with the beam, with 2' of drywall on each side of the joint. If a joint ends up under a beam like that, it cracks, immediately, then the crack opens and closes seasonally, with the weather and humidity fluctuations, rendering it unpatchable. Yep, this piece of helpful info. was learned at the school of hard knocks, as I have made this mistake before, and there is no solution other than digging the joint open and installing a commercial metal drywall expansion "V" joint where the crack was.