when it comes to AWS and ECS/etc there's nothing stopping them from transparently running MacOS containers on Mac hosts.
You mean apart from no support in macOS to host containers, or run software within containers? AKA point 1 in the post you quoted.
On the backend of that there's no reason why the docker engine can't use the native virtualization tools in Big Sur to run MacOS containers
I honestly don't know if you don't know what containers are or if you are trolling.
Virtualisation is literally about running a virtualised, entire computer. While it may know, it's running on virtualised hardware (i.e. if it's PVM), it's doing everything a regular OS on hardware does, from the kernel through to the software you install and run.
Containerisation is running programs in a different execution context, under the control of the kernel. On Linux this is built around cgroups. I don't know what the name of the API in windows for it is, but it's the same concept. The kernel runs some programs in isolation from other programs.
it would work functionally exactly the same way parallels et al can virtualize MacOS on MacOS in Big Sur and it's perfectly cool with the current Mac licensing to virtualize MacOS on Apple hardware.
.. So not containers at all, in any way, shape or form.
The main reason it really isn't likely yet
The main reason it really isn't likely yet, is that it isn't
possible yet, because macOS has no containerisation support. It's nothing to do with market demand or investment cost.
What *Apple* would have to do to make MacOS docker containers more useful outside of things like ECS, which is what I was mentioning "if they allowed it", really is to (legally, you can, of course, do this with hackintosh type builds) allow MacOS to be virtualized on non-Apple hardware. I don't see it happening but that was what meant.
Once again, you're conflating containers and virtualisation. Apple could send every person on the planet a gold-stamped letter saying "You are allowed to run as many virtualised copied of macOS as you want, on anything you can make them run on, including but not limited to a Whopper with cheese", and that would have zero impact on macOS being able to host containers.
all the pieces are there as of Big Sur for AWS to create ECS MacOS docker containers
No, they really ****ing aren't, and please stop making claims that you have zero idea about.