Isn't this down to the chipset?
The Nvidia shield has had an exceptional update cycle because Nvidia created the chipset and still supports it.
This has been a problem with Android since it started no matter what the device, phone, tv, or tablet. I have a Sling AirTV and it received maybe one update and I'm still stuck on 7.0 while there are now devices that are out there getting 9.0 and Sling has no plans to update it. It sucks being left behind and the article makes a good point about avoiding the Android TV and getting something like the shield to plug into your "dumb" tv because replacing a box is easier than a $500+ tv set.
Yes the Shield is a good replacemnt for a slow old Android TV OS - if you must stay in the Android TV ecoSystem.
But even that solution it is getting long in the tooth if you need modern tech support like DolbyVision, (Netflix) Atmos, HDR10+ HLG (for UK users) and high quality upscaling of non 4K content.
Plus then there is also 4K HDR YouTube and 4K HDR Play movies missing.
It's like being stuck between a rock and a hard place going forward.
What? I've got a Shield and have got 20 updates on the last 3 years
I thought this was well known among tech-savvy consumers. This is not just an Android TV problem, but a smart TV problem in general. The solution is to buy a TV with as thin an OS as possible and plug in your media box of choice. Those devices tend to be much cheaper and easier to upgrade than a TV.