1. Summer warmth: Having had to experience what the Arizona sun is like in mid-summer, and how effortlessly the Model S's pano handles it, I now have zero qualms about that factor wrt an effectively all-glass roof.
2. Winter warmth: Every last traditional vehicle out there is an insulative nightmare. If you ever take an infrared image of a vehicle, any vehicle, you will see it has the heat-retentive qualities of a sieve: windows, doors, seals, roof....when we were disabled in our F-350 a number of years ago with the outside temps at -51ºF, it fell to very close to ambient in an astonishingly few number of minutes.
But....it doesn't matter: take it from me, I know cold. And the #1 no-second-place best way to achieve warmth in a vehicle is not through the convective heating of the cabin air, but through the conductive heating of the seats. And, although there has been a small amount of criticism of Tesla's seat heaters, we've had no issues with ours and rank them at the top of all of our vehicles' seat heaters.
3. Sound: my considered opinion is that this is negligible. Not because metal+deadener+headliner isn't more effective than glass alone, but because the greatest incursion of sound is though seals and interstices. Sound deadener is terrific at diminishing intra-vehicular noise - for most cars, that's what's emanating from the engine and exhaust system - but the Model 3 will have effectively the same number of window seals, door gaskets, etc., as the next car and so what is or is not on the roof will be just noise in the data, so to speak. The greatest sources of noise in an EV are (1) tire noise - and there it's the efficacy of the wheel well jackets; and (2) wind noise - and there it is air grabbers like seals and joints that are the source - not the smooth skin.
4. Headroom: Tesla came right out and said the glass roof would provide more headroom than a metal one; I'm taking them at their word.
5. Perceived headroom: There is zero doubt in my mind that the effect of more glass is more capaciousness.
6. Dirt on exterior: Just a suspicion, but I'm guessing that if some bird splat is going to make you upset if you see it from sitting inside the vehicle, it is going to make you more upset when you're approaching your car from without and thus you'll deal with it. Moreover, the peripheral nature of most of that glass for most occupants means that you'll not really be seeing most or even any such infractions. And I for one have not heard any reports of Model X owners becoming upset because their own Prevost-bus-like windshield is becoming annoying because they see a squashed bug in their vision.
7. Privacy: Ummm...huh? Get a room, folks.
8. The one significant concern I have about glass is whether TM's supplier is able to get on the stick to supply in proper fashion the number of panels required for Model 3 production. And I am not able to envision TM not having enough experience and clout and good sense not to have that sticky wicket properly anticipated.
So...ceteris paribus, I'm voting for glass.
