Re: screw-on bowl?
That would definitely limit your options for bowls. You would have to have every bowl maker use the exact same thread pattern just to fit that hookah. Manufaturing variances aside, the added cost would be a big factor.
Straight male/female fittings and cheap grommets are much easier to make. Neat idea, but I think it would be more hassle than it's worth.
FroYo = Phatt Azzd Kaloudz Yo!