Yeah, a launcher with Android is like a shell in Windows. Windows uses explorer.exe as the shell, and it can be changed, but not on the fly. Kinda cool that Android allows the shell to be changed without a reboot. But I doubt we'll ever see two shells able to run at the same time, and be able to switch between them.

Doh, having said that, this is a Linux based OS so it's probably already doable, just not implemented yet.