Right now there's a weird tug of war between deserts being inhospitable wastelands and deserts having enough features for desert-based civs to use them efficiently, which ends up letting other civs use them too, even if not efficiently. What ends up happening in my games is that barbarian cities will develop next to oasis tiles, and when they start settling, the desert is suddenly a home to a live and well civilization, rather than being a no-man's land. I wonder if it would be too unrealistic to remove most oasis but allow desert civs to cultivate them in some way.
I'm glad you like the general idea. Though now I'm getting tempted to bring back a suggestion I made almost 10 years ago to require a new city to settle on a fresh water tile until reaching a tech that allows settling without one.