Both devices are prime examples of planned obsolescence products. While older AppleTVs- just like older Macs- would have the horses to keep right out producing their same output, the software on them will stop updating (both tvOS and apps themselves) until you basically must replace them, even for the same output. Fire up any vintaged AppleTV and see this first hand. Try to run the favorite apps and/or attempt to install/update favored apps to use new features offered by those apps. Or fire up an old Mac and try to run Safari or similar. It's basically over when the Corp says it's over... even if the hardware itself is still fully capable.
To me, HPs are basically iMacs for audio: a relatively great value "all in one" going in but doomed to "throw baby out with the bathwater" at the end. The dominant "dumb" part- the speakers themselves- like the iMac screen- will still be perfectly fine and should be able to produce the same quality of audio for 10, 20 or maybe even 30 years. But the "smart" part on which the dumb part completely depends to play anything will be obsolete as soon as that tier of Apple tech is arbitrarily vintaged.
Unlike old Macs where one can apply third party hacks to get around Apple vintaging for another year or three, these self-contained boxes without user access to the software probably won't have use-extending hack options. About when Apple decides it's time for you to give them more money, the older tech begins having problems and/or stops working entirely. Relative to HP, see this ALREADY in how Gen 2 could not stereo sync with Gen 1. Will Gen 3 sync with Gen 2? Precedent implies no. Why sell you only 1 new speaker when such choices can drive the sales of two? 💰💰💰
And yes, since ASD also has a dependency on a tier of iOS software & silicon, I'd be worried about those too. People are still using former Apple-branded monitors discontinued from 12+ years ago because they are not married to iOS-based "smarts." Everything newer that leans on iOS and a specific generation of silicon likely has a ticking clock until they are made obsolete, whether they still have the ability to deliver their core benefit(s) or not.
For something priced like AppleTV, a buy of the latest today probably gets you 5+ years of full use. For something priced like ASD though, the same 5+ years of use is a bit more expensive.
Caveat emptor!