you've been able to get a list of running apps since at least 10.4, and this is already in QS in a couple of different forms.
if you enable searching catalogs, and enable the "Running Applications & Processes" catalog entry, that will show you a list of running apps. also, the "Visible Applications" proxy object shows the same apps.
this actually seems to be a bug, Visible Apps is meant to be a counterpart to Hidden Apps, but it shows all running apps whether they're hidden or not. in the next day or two, i'll fix this bug, and make a "Running Applications" proxy that does what the Visible Apps one does currently