I started a duel level as this sometime ago. The issue is that in order to get a realistic looking environment you need to have clarity, and see beyond to the various bubbles and lights, if this is done via brushwork it will be unplayable. If this is done via a skybox... Well let's just say it would have to be the best Skybox in the history of Q3A for it to even resemble the gungan city enough for folks to recognize it.
It'd have to be a downright inhuman skybox.
I don't think it would be entirely possible as a single player level unless you seriously compromised some of the architecture.
Good luck to whoever tries it, don't say I didn't warn you.