At first sight it looks like even more work than the original "switching between folders" option.
Since you mention Deleted Items... If I delete a message, it goes there (and Deleted Items can be emptied via right-click, as with local folders). If I move a message to a local folder, it doesn't go there. In both cases the message gets the strike-through, remains in the local shadow of IMAP folder (with option to undelete it), but doesn't exist on the server anymore.
It's weird there's no other sane way of purging it, apart from when switching between IMAP folders...
Well, I came up with another workaround, I'm just not yet sure whether it'll work or not: I set up a filter (or another condition) on the Unified Inbox view, which will hide the "deleted" items. In addition, I turn the "Purge items when switching folders while online", so they actually get purged "casually" when I do click around. Thus, I get a clean Unified Inbox view, plus the messages get deleted eventually.
Do you think this would be feasible? Which condition or filter should I use for this (I played with IMAP Status and Remote Status somewhat, but it didn't work out the way I thought it would)?