There is an extra level of menu selection required for selecting track input compared to output. Is there a way to make the input dropdown like the output dropdown (see below)?

If you now open Addictive Drums, it adds a further 40 input options. Add a few other synths to that and now your scrolling up to 100 inputs.

even indenting the L/R underneath the stereo would make the list easier to read!

Quite the opposite, I'd prefer if the output menu also had a "cascaded" option for "physical outputs", "buses" and "plugin SC inputs".

When I have a bunch of plugins open that support sidechaining, it becomes a menace to navigate the output menu.

inputs? outputs? the whole shebang could do with cascaded submenus! :-)
 

I'm with the OP. If I'm recording an audio track it is one of two inputs - left or right.

Marshall
I'm with the OP. If I'm recording an audio track it is one of two inputs - left or right.

But this is just for single sources. You may have stereo room mics, a stereo external synth. With my AD2  example, I set up everything to com into sonar's mixer as monos exept the overheads and room mics, I do not use the Main stereo outs. SO from one VST I need to use both stereo and mono.
 
The audio ins are more than just the sound card, internal options are cr4eated as you add them. 

Cascading is better when there are a lot of items in the menu. A single list is only easier if the list is short. I vote for cascading.

I cannot see any other way they could do this. 
If they hide the first list there would be a lot of people yelling at them. 
Possibly there is a way to use Keybinding to macro the action? 

Track templates?