This can be hardware or software:
Personally i like to see a steinberg midi keyboard with mounting option for your cmc controllers.
I would love to see a monitor controller from steiny / yamaha. Not with audio card build in, only the controller part 
a “little” cubase for IOS
I’d like to see a drum modeling VSTi for drum sound generation. Not just a cheesy virtual sound a’la TR-808/909 or a sample player, but real modeling. That, in my opinion, would be fantastic!!!
I would like an equivalent of Steiny’s MR 816 series but with, at least, one MIDI I/O implemented. Still don’t understand why the present ones are lacking this essential feature : how are we supposed to use MIDI gear beside this ?
With a midi interface. For me I really don’t care if an interface has midi IO or not, as a single in and output are not enough anyway. Buy a decent midi interface if you need Midi, if it’s the single IO you so desperately need, that’s another €10,- to M-Audio and you’re done.
More MIDI files in the sample library.
We find the drum loops ok for quick work but would prefer to use editable files.
They are clever but too unique and sophisticated unless you want to use loops that thousands of other people are using worldwide.
It shuold be asy to do and I don’t know it has not already been done.
I’d like to see .Net “Editor” plugins, for expansion of the editing capabilities in Cubase.
So for example, just like we have VST plugins, we could have MIDI Editor and Audio Editor plugins. If someone creates a better Piano Roll editor, you can use that one instead of the built-in one. Or someone might create a better Logical Editor.
Also, Import and Export plugins would be cool.
Anyways, you see my points.