1) eliminate touchwiz
I could just stop here, but for discussion....
2) sell it unlocked so I don't have any carrier branding/bloatware
3) remove or give the option to uninstall all bloatware
3) move Samsung logo to the back
4) front speaker
5) 3500+ battery
6) don't delay colors or limit them to Note. That emerald green should've been available globally at launch. and like you said, titanium silver would be killer.
7) swap the rear glass with something else. I actually prefer plastic, but more nexus 5 than S5 kinda plastic. anything but glass.
processor, RAM, display, camera, etc .... all that is perfect. I don't need more specs at this point. say what you want about the S6, I was using my mother in laws today and 95% of it is awesome. they hit it out of the park with that processor (not to mention the money they'll save/make on them), the camera is ridiculous, and that gorgeous display. I'm not a big aesthetic guy, more into UX and optimization, but damn that phone is nice looking!
and I don't mind no SD anymore, 64MB with DropBox is good enough (for me)
I realize this won't happen, but it'd be a dominate phone.