I wanted to do this and got a Shield last year but returned it because of a live TV bug with the Android Plex client. The programming guide stopped working and could only be fixed by restarting the app, but on Android quitting to the home screen keeps the app running and you can't force quit without going into menus. Sadly that's the OS and changing a launcher didn't fix it.

Actually you can double tap the home button on your remote to see all apps currently running, and can then click the close button on any one of them.

Google TV apps leak memory like a sieve, so it's pretty common to need to manually close all other apps to make the one you're trying to use work. Even !y wife just dies of now as soon as any one of the apps starts acting up.