Would be great if you could play from the internal sound card in internal mode, though not necessarily for performing...

Even if it was only one deck.

That way, you could set your cues and loops, etc, while you listen to you music, giving you more flexibility in preparation, and less reliance on 3rd party apps (itunes etc) as SSL would serve as it's own player.

It's already a decent tag editor, this would go one step further in eliminating any middlemen.