One of the thing I prefer is the eraser back on top. I prefer turning my pen around to erase just like I would with a pencil. The Surface pen from the Surface pro 3 should work with SP4 so if you don't like it you could always get that one (although I don't know if it can invoke Cortana with a long push and it has less levels of pressure and non-replaceable tips)
But like you said, i'd like to see the fingerprint scanner on the other coloured covers. I know the camera supports windows hello on SP4, but fingerprint adds a second method and those coloured covers look so nice

I'm impatient to see how the new teal option looks!