This situation irritates me (perhaps more than it logically should) ... We own two of the 3rd. gen. Apple TV's in our household, and we considered upgrading to the 4th. gen. -- except realized it just wasn't financially justified given what we do with them. (We already own an Amazon Fire and have a Prime subscription, so a lot of our movie or TV watching happens on that unit. We also own a Roku 3 that sits on the big TV in the living room. It, honestly, doesn't get a *lot* of use, but it runs Plex so it can talk to a dedicated Plex media server I run - and that justifies its existence by itself.) The AppleTVs are both on small LCD sets in bedrooms and mainly get used if someone wants to watch NetFlix on one of them, plus the ability to AirPlay to them on rare occasions that's desired.
I had hoped that support for HomeKit would be extended to the 3rd. gen AppleTV with the new "Home" app, since Apple didn't say much of anything indicating otherwise. As they cost a lot less than 4th. gen models, it would actually make a lot of sense if Apple kept them available *mainly* for HomeKit hub purposes. I get that right now, it's only the Home APP that's not being supported -- but that's still a piece of the whole HomeKit eco-system, the way Apple envisions it all coming together.
A lot of people got screwed over already, when Apple announced that a lot of home automation gear people ASSUMED would be compatible was in fact, NOT, thanks to not having a hardware chip with enough bits of security encryption to meet Apple's requirements for the standard. I knew people who spent hundreds on EcoBee 3 thermostats, for example, only to find out they had to get rid of them and buy them over again to get the HomeKit approved editions of the same things.
(I *think* my Chamberlain MyQ garage door opener has one of the Broadcom chips in it that's actually HomeKit compliant -- yet so far, no word of it getting HomeKit support either.)
This entire HomeKit roll-out has been a mess, IMO. Apple released something half-baked and then slowly improved it without much explanation of what was going on. You had to be really into home automation and following multiple blogs and support sites to figure out the status of all of it.
read people, its just not home app compatible, it never was !