Have had most of the atvs, and have extensively used them. I think the services are great and love the way that little tangents have been added like the way you can control the ATV with your tv remote, HomePod theatre audio (if you have homepods), ATV remote control from the iPhone Etc. It’s interesting to see how many features have been adopted by rival devices; google tv even looks very like the ATV menu.
But the ATV app is available on newer TVs, and largely make the box redundant. I think this app could get even better, and fulfils most of the important functions of the ATV. I don’t know what a new ATV could even offer, but there’s nothing compelling about a slightly faster processor or gaming services (for me anyway). If the app could be better integrated into third party TVs, so that I can still use homepods as a sound bar, I think there is some mileage left in it as a service. I’ve got airplay 2, HomeKit and ATV+ on my Sony, I believe some tvs (LG?)also have Apple Music. Siri could also be added (maybe) and support for multiple users in software, but because of the way homepods work hardware would needed to use them with the tv (maybe there potential for a relatively cheap device to airplay to the homepods). For me, a new ATV would need to offer a lot more function to make itself worthwhile and the way things are atm with the world the less devices using power the better.