Camkeyd is stuck in devel and is deprecated, superseeded by shortcutd. There are no apps that directly switch because holding keys is hard on N900, as Windows Alt+Tab does the same (launch exposee), only it helps you select by releasing a key. On N900, it would require you to hold a key, then hit other keys which is quite a pain.

Use shortcutd and tap the app you want, it's what we all do and it's quite useful once you get the hang of it. Since there is no "default app" in exposee, you would need a different exposee to implement a "current" window.

I doubt it will be done, or its usefulness. I'm sure the devels of shortcutd are open to suggestions if you have a good one, though.