Hey there @lennonc welcome to the community!
I believe at the time of that post Node 16 wasn’t planned to be supported in Rules, but that has since changed. Since node 16 looks to be supported until 9/23, I would say that’s a good date to target. However, I believe (don’t quote me on this) Node 18 will eventually be introduced to legacy extensibility (rules) as well. While it’s definitely recommended to migrate to Actions when and where possible, there are still some feature gaps that need to be addressed - Because of this it is still completely safe to use Rules, and you can expect much clearer communication here in the community when there are any further developments.
Cheers!