Thanks for the feedback
I've tried red oak, and it does wear..it tears up at the open
spots..and if I fill it..well the filler is quite soft. Maybe white
oak would be better? Or a harder closed wood like ipe or maple, and
then use a rubber center tread.
The nice wood does seem incongruous with the use, but the stairwell is
open (no doors at top or bottom), and well, I'd like it to look
somewhat nice.
I was also thinking of stone or concrete (thin stone slabs like one
might find in a garden application).
Jerry