Why can't I program my 3rd party remote to access the "siri" and/or "home" buttons? I can only program a 3rd party remote to access navigation buttons, select, and menu.

There is no mic on 3rd party remotes for Siri to work. But I do have "home" programmed into my harmony 1. You should send feedback to your remote provider if their remote doesn't work with new devices...

You actually got the "home" button to work with your Harmony One? (not the "menu" button, but the "home" button with the little TV icon). Did you use the Harmony application to program your remote?

My understanding is that Siri and the Home button use Bluetooth, thus they are not controllable via IR remotes, like your Harmony One.

I hope you're right since I loathe the Apple TV 4 remote control.

Actually, after a bit more investigation, the "Menu" button (which is easily mapped to IR universal remotes) can act as a real "Home" button simply by holding it down.

You would still need the ATV 4 remote to do app switching and put the ATV to sleep, however.