WOW! After I clicked on your drawing, I realized what a great depiction it became!
I had an identical problem when building my pool room. The "obstruction" in my case was also stairs that encroached the imaginary lines of cue stick impingement.
However, given that the stairs, assuming a six-inch rise per tread, do not actually become a backstroke impediment until they rise to the surface height of the table - which is 30" - the shooter may stand, kneel, sit or crouch on those stairs - since they are a fixed component of the room. But the stairs themselves don't prevent a normal stroke with a normal stick in any case, as shown in your drawing.
I'd stick with the 8-footer option and play around a bit with final table placement, minimizing wall to stick butt conflicts and minimize or fawgettabowt the minimally intrusive leg, foot and body obstacles of the shooters when shots from atop the stairs are required.
If I can see the table and the shot, and my stick has no rearward obstructions, my body position is secondary, especially as shown in your drawing.
I have one wall that when shooting a "stuck-on-the-rail" shot - is 1" "in the way" of the wall when holding my 2" over standard length stick dead flat. I overcome the conflict by going to a 15º stick rise and picking up an inch or two of "clearance" avoiding a wall tap on a normal backstroke. Of 100 or so shots, I might encounter a level stick wall conflict 1 or 2% of all 100 shots.
Of course, I could switch to my normal shaft, reducing the stick length by 2" but I prefer to play around the conflict, rather than change shafts.
Let us know how it goes - please.