Nova is a mobile launcher, it does suport remote navigation but would be a huge pain to setup and isnt worth the time.
I just keep the default launcher for AndroidTV but if i ever get a shieldTV and Oreo i dont know if i will like what google has done to it.
Lots of people suggest HAL Launcher, its as close as you can get to the default AndroidTV launcher but you can customise it.
You have two choices:
Stock - Smooth, but doesn't have enough customization. Google should have allowed us to add custom rows and hide apps, that's my biggest problem with the stock launcher.
I've used Oreo's launcher on my Nexus Player. Again it's good but customization is lacking. I only messed with it briefly but was shocked I was limited to how many apps to show on the app row (6.) As limited as it is, it's nice to display the apps you use most on the home screen.
HAL Launcher - Great at customization. Biggest feature is ability to show sideloaded apps with no extra work on your home screen. It's good, but after using it for a week it didn't feel as good as stock. I would try it out and see what you think, you might find it works for your needs.
And I'll add (while not perfect) Kodi: You could run Kodi as your launcher (sort of.) When I had an android box XBMC Launcher let you start your box in Kodi. I don't know if it works anymore (it was taken off the Play Store.) But you can launch Kodi go into programs and all your android apps are there. When you launch an android app from Kodi, most exit back to Kodi. With a skin like Titan, and the smart shortcuts add-on you have a lot of flexibility to customize Kodi to your liking.
Just a quick look SPMC can auto-boot on the Shield https://github.com/koying/SPMC/wiki/How-to-autostart-SPMC-on-boot not sure about Kodi.
Just something to keep in mind.
I've been using Yahoo's Aviate, and I can't use another anymore
Would love to see people post screenshots of their custom launchers to see how people have them set up. Not found anything yet that works as well on the TV with a remote as the stock one but hate how little option you have to make it your own.
Nova.
Another vote for Nova Launcher.
The stock one