I keep thinking about the 4-finger swipe ... but then I realize it can severely limit the device.

On a large (10") size, there are possibilities for some "fun" games that implements four players (like 4 player reactor) ... and if all four swipe in the same time it could accidentally trigger the app-pane and kill the buzz.
And that's one example, think of how many other things could possibly be limited.

I think a better management could be to smartly assign secondary functions to the "Android buttons". From left to right, we can have Back, Home, Menu.
Hit Back and it goes back a page/watever inside the App. However hold on it for 1.5seconds and it should kill the app (no ram wasting) and get you on the Home screen (MIUI Style).
Hit Home and it gets you back to the Home screen (MIUI Style). However, hold the Home button then it gets you to a listing of all the Apps you opened (background tasks stay hidden) just like in Maemo.
And then when you hit Menu it will open that App's contextual Menu, and it will also make the status bar appear if it was hidden (eg if your watching a video, hit Menu quickly see the time in notifbar, hit Menu again to hide it).
When you hold the Menu bar, it again brings the notification bar, but it should trigger the Search function, so the text box is also activated on the top, and the onscreen keyboard appears. Now this Search will only search through the app (ie a keyword in a message if your in sms) but you should have a little button on the side of the text box which opens a list for you to search (within the App, within the phone, Google Search, Maps etc).

Now this is dependent on the device to have the three buttons on the bezel. If they are missing then the same concept applies, except the notification bar becomes much thicker (Touch friendly) and it incorporates the "Android buttons". And so the Satus bar in the slate would need to be always on (like 100%) and placed on the left edge when in andscape mode, looking like this:
____
[l___] <Tablet
^Status bar