After looking at the OP's list, I do agree that some of the items listed would be desirable; others, not so much...
The Mustang would be a far better car with simple additions such as:
1. Heated mirrors. It really annoys me that I need to manually defrost the mirrors especially when ther's precipitation;
Never really needed them here in FL, and they're optional on '13s.
2. Glove box LED lights;
Would be nice to have ANY illumination for the glovebox (and for that matter the center console storage box; they stick LEDs in the cupholders which I actually put cups in maybe once, twice a year, but my center console box sees almost constant use and is left in the dark? Come on!!), period. Heck, my '95 Z28 had an illuminated glovebox...
3. Trunk lights (2) on the deck lid;
Would be nice to have, but I'd still rather have an illuminated glovebox and center console storage...
4. Sun visor that blocks the windshield behind the rear-view mirror;
Never had any issue with the Sun in that regard.
5. Transitional glass rear window that darkens when subjected to the ultraviolet sun light;
Fixed that issue when I had my windows tinted...
6. More durable driver's floor mat;
Would be nice, but I believe there are quite a few heavy-duty OEM and aftermarket floormats out there...
7. Lower body moldings to match the body color;
Already done on the 2013s, and personally I like how the lower moldings look with Sterling Gray.
8. Wheels with an avant guard accent color;
If 'avant-garde' means anything like having banana yellow, pistachio green or similarly garish colors, by all means make it optional. I'll have no part of it, however...
9. Tilting head rests;
As stated by others, it was fixed on '13s. Never had issues with mine, however.
10. Side and rear proximity warning devices;
If people feel the need for these devices while driving, by all means make it optional. But my rear-view/side mirrors and my cranium's ability to swivel have served me well in my 16 years of driving and I certainly don't see it as 'must-have'.
11. Turn signal audio tone with adjustable volume;
Ehh....maybe when I'm eligible for senior discounts I'd consider it to be a must have...in my Buick/Toyota/other boring car to drive when one reaches such an age and/or doesn't care about driving.
12. Transparent Mustang Pony in the front grill illuminated by My Color LEDs;
I do believe that there may be certain legal issues with such an illuminated symbol, not to mention it would look incredibly tacky (IMO, of course).
13. More accessible USB port with a miniature flash drive;
Would be a nice feature to have, especially for playing MP3s.
14. Built-in front looking video recorder;
I have no desire to embarrass myself on Youtube, thank you very much.
15. Bright color brake calipers.
No. Just...no. I'd much rather Ford fit larger rear rotors on Brembo-package cars with black rear calipers to better compliment the larger front rotors and wheels, if only for aesthetic reasons, not functional ones.
Digressing just a little bit here, what I'd like is for Ford to offer more...you know...CHOICE
...with regards as to how one can outfit their Mustang from the factory. While I'm overall pleased with mine, I absolutely despise the fact that due to a couple options I wanted, namely:
- Premium interior (the Base interior turned me off almost as much as the Camaro's)
- HID headlamps (Yeah, they're standard now, but weren't for the 11s, and did they really have to force you get the security package to get them?)
...I was basically left with no choice but to order a Premium, which had several items I really DIDN'T
want, such as...
- Leather seats (over time, I've grown accustomed to them, but I'd much rather have cloth Recaros any day of the week)
- Sync (I have no cellphone [seriously] or any iToys, thus I haven't used it once since I bought the car)
- Shaker 500 audio/SiriusXM (not that much of an audiophile, have no desire to let people sitting in traffic know what my musical tastes are, and I hate the damn plastic wart that's sitting on my trunklid)
...which left me with a slightly bitter taste in my mouth when it came time to order (although I'm well aware that Ford is far from the only mfr. to do things like this). I'd wish Ford would just ditch the whole Base/Premium trim level scheme and just offer one trim level with more varied equipment packages (and the ability to order features from these packages as a la carte options if certain other features from these packages don't match their needs/wants/budget) to cater to differing customer tastes.