Didn't work. I took my angle grinder to it for a good 45 minutes, but the area cleared by each pass was way too narrow to make much of a difference, and it took multiple passes to get down to bare wood again. While it could give the bare wood a new, rougher texture, it still didn't turn out nearly as good as the original.
Don't even think about trying this with a handheld wire brush; you won't get anywhere.
In the future, I'll simply by a new piece of plywood or rely some sort of floor wax to get the proper surface.
And yes, I'm actually holding that handstand. Get on my level.