Curious on this, too (also in AZ).
The only data point I have: a friend of mine from Palm Springs bought a new Model S 75 last year and says the dark tinted glass roof is a non-issue. He told me that on really hot days, he uses the remote cabin pre-conditioning to cool the car down anyway. He bought with the white interior to reduce heat gain, but kind of regrets that as it shows dirt quickly. He believes the majority of the heat gain is really from sunlight entering through the windshield, heating up the dark dash (necessarily dark to reduce glare), and the radiant heat being trapped due to the IR-blocking nature of the windshield. We need one-way IR blocking glass, it seems.
There was some speculation here that the non-premium 3 will still have a glass roof, but that the inside will have a permanently affixed headliner (presumably with an insulation / reflective layer).
Looks like Tesla sells a clip-in light-reducing screen for the glass roof for those that want that. Might make a good summertime option.
