I've replaced the Leanback Launcher with
Nova Launcher (version 3.3 as it works better with the controller than 4.0). With a little configuration you can get it to look and work really well on the Shield.
Nova lets you create shortcuts to any activity on the system, so you can still put shortcuts to Android TV-specific apps on the homescreen. You can also add a shortcut to the Leanback Launcher activity to get back to the main Android TV interface if needed. Or, you can set it up so that pressing the home button while in Nova Launcher takes you back to Leanback Launcher (so, press home button once for Nova, home button twice for Leanback). I can post a tutorial on how to set this up if anyone's interested.
I'm also using a Bluetooth mouse with my Shield, but since Android TV has no on-screen navbar,
Simple Control works very well for adding back/home navigation buttons. (You have to activate it through the Android TV accessibility settings, as running the app directly doesn't seem to work correctly for setting it up)
WIth these two apps installed, running sideloaded apps on the Shield becomes a much more pleasant experience