We ripped out everything under the stairway - took it down to barebones.
Drywalled, added outlets and a light. Let me tell you - drywalling all those nooks and crannies was not fun.
It's a perfect place for the treadmill. Out of the way, utilizing dead space.
I purchased these nifty gizmos for hanging my monitor.
Added a collapsible desktop.
I knew the area was going in so I reinforced the area with extra 2x4 framing.
You can move the desk out of the way if you're on for a run.