Great Ideas!
I think I never ever used the dropdown item list for the last 5 or 6 years. For me, it could vanish completely - for involved scenes, I couldn’t imagine a more cumbersome way to access things 
The Flat Item List is fantastic, Maybe a different way of showing hierarchies could be established that doesn’t take much space, like a kind of colorcoding in the background?
Or using the lines between the objects in different lengths to hint at their hierarchic depth?
The thing I like about the Sil3 design is, that you can keep your mouse in a similar area for all the keying. He has used the current layout basically and just moved it below the world view, but I’m sure one could create a much narrower layout while keeping the overview.
So with starting anew and concentrating on what is needed and less on what’s already there, I’m sure you could reduce the height by half.
- The command line at the bottom could be optional?
- The slider Area could be combined with the frame-ruler area - no need to have it twice.
- The introduction of timeline markers would also go to that new Slider/Ruler/Marker area.
- The In- and Out point fields could be integrated into that Ruler too (left and right)
- The current frame field could vanish if you could double click the number on the Time Slider to enter a value. This could also be an alternative option for the In/Out sliders.
- A better design for the transport buttons could integrate them better.
- Make preview belongs in here too with an options button that brings up a flying preferences window. The play tab could vanish in the long run IMO.
It would be interesting to learn, which Buttons are never used by anyone…
For me, the whole Edit: Row of buttons could be replaced by shortcuts 
Well I’m in spring cleaning mode 
When my current jobs are done, I feel like photoshopping too 
Very interesting thread indeed!
Cheers,
Edit: Yes, Blender could take a huge market share off the commercial tools if the UI would be more standardized… 3D is complicated enough - learning a completely new interaction model is too cumbersome for most people…