The Nexus Player's November patch includes Google Assistant so if you still own one of these Android TV devices then you'll be able to use Assistant for various tasks and queries, like playing something on Netflix, ordering a pizza, turning on or off the lights or asking questions about a specific topic you wish to know more about. It's possible that if you don't have the most recent version of the Google app installed on your Nexus Player that Google Assistant may not show up even after the November patch, so it's worth keeping in mind that being up to date with the Google app may also be a requirement for having Assistant present and able to serve your needs.
So far Google Assistant has only been available via the NVIDIA SHILED when it comes to standalone Android TV devices, but it is also available on some Sony Bravia TVs with Android TV built-in. Other than that, Google Assistant has been limited to mostly smartphones, some Android Wear watches, and of course the Google Home and Google Home Mini and devices like the TicHome Mini, a third-party smart speaker. It's also supposed to be showing up on tablets soon, though there is currently no time frame for release onto tablets.
With the Nexus Player now having Google Assistant integrated into it with the latest security patch, this may be the start of more Android TV devices getting Google Assistant as well. It's important to keep in mind that the Nexus Player is a Google device, so it makes sense that Assistant would show up through a security patch and Google app update. For other Android TV devices, it will be up to the manufacturer to incorporate Google Assistant into the device through updates, which means that it's unclear how long it could be before more Android TV devices have access to the digital assistant feature. If you're not keen on waiting, perhaps Google Assistant is incentive enough to consider picking up a Nexus Player somewhere if you can, or opt to grab an NVIDIA SHIELD. Of course you could also simply use it through your phone or smart speaker too.