Black Pro Model
New iMac design (even if thicker, if better ventilation or liquid cooling)
I doubt it'll be thicker and if it will, it's not much. Liquid cooling is for extreme computers which Apple doesn't manufacture.
Silent Running
It is already
Matte Screen Option
Needs redesign
Faster processor
That's more than likely
Better 24 LED monitor
Maybe.. I doubt we'll see LED unless redesigns iMac
Backlit keyboard
+ New Mighty Mouse = I'm buying
Minimum 8 GB RAM
Unless Apple adds 2 more RAM slots (total of 4) it's not gonna happen.
Better Graphics card or cards
Of course
USB 3.0 ports (and more of them)
Not yet.. More than 5 would make it look like cheese with holes
Absolute quality build
For company size of Apple, it's impossible