Forgive me if I'm mentioning the obvious here, but I have a 2011 V6, and haven't been inside the 5.0 in a few years...
I recently sat in a new GT that had the Raven interior. The first thing I noticed was the quality of the leather seats. The seats felt like they belong in a Lincoln; they're very soft to the touch. I looked on this forum and on Google, and no where did I see anyone as impressed as I am with the leather. I hope this is the same quality leather as the Premier Trim? Did the 5.0 always have seats like this or did Ford really step it up with the 2015?

 

Ford at least in the few mustangs I have owned has had very low quality leather compared to say the 2k lexus I owned a while back. The Lexus had 160k on the leather and it looked much better than my 40k mile leather in my stangs. I hope it has improved since the 05-10 models. Another complaint I have about the seats is the lack of side bolsters. the seat is pretty much flat.

 

I drove a premium 15 GT with the premium trim package. I was in shock of how nice the interior and seats were. Like you said, very soft but extremely supportive. No need for the Recaro seats anymore.

 

Dude! I went and checked my local Ford and they only had a V6, but it was in the color I was really hoping to see (Triple Yellow) and those seats have as much, if not more, bolstering than my 13 Boss 302 Recaros! I was quite impressed.

Also: It's about dang time Ford had a real yellow on Mustang. RIP: Screaming Yellow...