It would be extremely productive to have Alfred quit all apps except a particular one... Or two...
My take for this would be to incorporate the following commands:
quitall except "App name"
quitall e "App name"
Alternatively, one could type current to prevent the current app from closing.
Also, one could type many apps separating them with a comma:
quitall e ---App name---, ---App name---, ---App name---