I dig DCwebman's mock-up.....
Personally, I never us "Start" (never really found the Start stuff very useful on MC) but logically it makes sense to have it at the top, if it's going to exist at all (you don't start at the middle or end, you start at the beginning, eh?).
PlayingNow definitely needs to be at or very near the very top .... There's probably nothing that I click on more often. (I've turned off the "jump to playing now" option on MC, because getting sent to playing now automatically drove me crazy when I was trying to do other things in other areas of MC -- but when I'm ready to go to Playing Now, I'd certainly like it to be easily available at the top of the menu).
I also love the old "All Media" view option that the old MC's used to have -- there was a way to get that back into MC 11, so I added it back in .... hopefully will be able to do the same with MC 12.... but I've never really understood why All Media is no longer a default option on the tree....
(Note: I do use the Action Window items quite a bit when mass-tagging files and checking info, etc.... so I'd never want to see AC go away ... but I wouldn't mind if the AC was minimized by default, either... either way would be fine by me ... But having MC remember how you had things set last with these would be good.... But here's what I'd realy love: being able to expand the Action Window's sub-windows upwards ... this would be ideal ... the Tag Info action window, for instance, requires a lot of scrolling if you're looking at all the available tag fields, so it'd be great if you could click an arrow that would maximize it vertically, covering up the rest of the tree when needed.)
Other than that, the new MC tree is looking good.... shaping up nicely, I'd say!