Fact: Tesla has two cars with glass on top.
Fact: Some Teslas are bought and sold in sunny places.
They do have experience with this issue.
I was concerned about the issue before I got my Model S. I do not have concerns about the Model 3 I have ordered because I believe and have experienced that Tesla knows what they are doing about this issue (as well as many others).
I own a Model S with a panoramic roof. Wouldn't trade it. No problems. But I was concerned about the possibility of too much sun in the summer months, so I bought the sun shades (from Tesla). They pop in, fit nicely, look nice. That may not work for everyone (the popping them in, which took about one minute per panel, once in the early summer and then out in late summer.)
(I have some pictures, but can't get them posted here.)