On the topic of a metal roof section as a cost saver for the 3, I don't think it could be a cost reduction.
1. Requires new stamping die for one special part. $
2. Requires press run time. $
3. Requires painting which can't be done with the rest of the body because it's a separate part and adds to VOC allotment. $
4. Requires a different headliner. $
5. May require different robot handling and different adhesive
to install. $
6. Must be matched to the correct car as it goes down the line adding complexity and inventory headaches. $
Conclusion; not happening ever.
I would possibly dispute point 4 as the non-PUP vehicle might have a different material headliner anyways even if it's the same shape (though seeing as Alcantara / Ultrasuede is already gone for some time, I'm not sure how less premium you can get... ), since in theory non-PUP should have less "premium" materials
5 I might dispute since if they do stick with metal roof non-PUP, the most obvious way to install it would be to install it in the exact same manner as the glass roof. Shouldn't be hard to design it in such a fashion.
6 they probably still batch colors right? so matching isn't that hard except when they transition colors now and then.
While I do suspect that overall, it's not worth it purely from a cost savings perspective, I think the biggest gotcha is going to be the paint issue.
Perhaps some sort of fixture that sits in the vehicle to hold it as it goes through the paint line and it gets sprayed somehow, then it gets taken out, but then we go back to matching them up again (#6). If they do it, then I think the most sensible paint solution is simply to have a car-sized fixture that runs a whole batch through together which then get set aside for later installation. If the fixture can hold 8 (for example), then run 8 non-PUP designated cars through the paint line, followed by the fixture with 8 panels on it, repeat. That should at least get the shade close since they're sprayed close in time to each other ...
But again, I suspect it's not worth the hassle. Possibly they offer it anyways, and it's not a cost saving measure for production (but the glass is only offered in PUP and thus an upsell for margin anyways), and the main reason to offer it is just upselling to PUP and to provide the option for those that really want a metal roof (though considering how little of the roof will be metal, it seems pointless).
