The ability to change realtrack instruments (or styles) within a song, in other words: going into the bar setting and changing the bass from "funk finger style" to "walking swing" (probably not possible because of the loading time involved - unless it loaded everything at the beginning of the song)...

I'd also like a nice "bossa then swing" real track. Right now I've got a pretty good workaround by loading "bossa then swing" in "tracks with real drums" and adding the realtracks: bossa piano and sw acoustic bass (the bass does pretty good on the "A" part in 2 (sounds like he's playing in bossa) then "B" comes in with a great acoustic walking bass. The bossa piano throughout the entire piece works too. It sound good with A Night In Tunisia...