Honestly, I would far rather see instead of a setting book "Al-Qadim", a cultural book "Arabian Adventures", with the tools (prestige classes, feats, races, monsters, magic items, etc.) for creating a wide range of arabian-themed adventures and settings in 3.5E D&D.
Thus, the players who have Al-Qadim can use the rules elements of that supplement to enhance the material they already have.
Meanwhile, the players who don't have Al-Qadim can use it as source material for their own campaign setting.
Perhaps a couple of Al-Qadim references can be used as source material - as for instance the City of Brass and Sigil were referenced in the Planar Handbook - but the entire work isn't so tied to one setting that it can't be used elsewhere.
I would think that the approach I suggest would be far more useful to us.
Cheers!