Back in college, we used to play 'latrine ball' where everything
was in play (use your imagination). It didn't detract one iota
from the enjoyment of the game.
So, what if shots off the overhead curtain were to stay in play? Why not?
While we're at it, can you think of any other 'impediment' you might add to the court? For example, how about a small foam rubber 'pillow', say 1-foot square, in the front corner about 6 feet high, Hit it and the ball dies - you win the point. But, miss it (while trying for it), and you're dead meat.
Any more brainstorms?