I'm shopping for TVs and I'm wondering how updates and such work. Is it up to the manufacturers to provide updates, similar to third-party Android phones? If so, are any of them particularly good about this? Wondering if I buy an Android TV today if it'll be likely to be updated to Google TV.
Or would it be better to get the new Chromecast if I want to get timely software updates?
TV Manufacturers aren’t going to provide constant updates. They make money by selling each TV, so there is no incentive for them to provide constant updates.
If you want the latest Android TV at all times, I recommend Shield TV Pro and maybe the new Google TV dongle.
The only Android TV Manufacturer I would trust to provide timely ongoing OS updates is Sony, but you have to be real careful about which model TV you buy. (Currently even some 5 year old models are getting OS updates)
The 2020 Sony X900H/X9000H TV is the 2nd most powerful Android TV device you can buy - after the Nvidia Shield. But even then that Sony has better HDR (HDR YouTube/Play Movies/TV) and Apps support (eg Apple TV App) vs any Shield. It even has Airplay2 and Apple HomeKit support. Basically it has everything.
Google TV is coming to specific Sony (Android) TV's and others in 2021:
https://www.flatpanelshd.com/news.php?subaction=showfull&id=1601497728
The big advantage with such a TV setup is Motion Control and Picture Processing for smooth video playback is MUCH better on a Sony TV vs any external media player you can buy - that is what you pay extra $$ for.
I expect the powerful MediaTek MT5895 is what Sony are going to be using for a long time going forward for Android/Google TV.
Apps updates are up to each individual Android App developer, nothing to do really with the device vendors.
You really do not need any other Android TV device with such a powerful chipset X900H TV setup. It's snappy with no lag.
https://forum.kodi.tv/showthread.php?tid=356128
Personally if I did not already have any Android TV device AND needed a new HDMI 2.1 Android TV I would have no hesitation in getting a Sony X900H. It's a game changer for the TV - Android TV ecoSystem.
I wouldn't trust the TV manufacturers to keep up with updates or in a timely manner. Buy the TV with the best picture you can, and the android TV dongle, stick, box, cylinder, or cube of your choice.