why would it be any more prone to getting rootkits in the kernel than any other process that was granted kernel access to do "this thing you think you need to do"?

How so?

On trusting trust

How would you be able to root out these containers doing seemingly anything sitting in kernelspace?

The code wouldn't be running in kernel space, just the setup/configuration of the environment, which really isn't any different than it is today, tbh. This seems to be more about attaching a kernel auditable id to a container.

It sounds like what you are talking about is already existing functionality, not the proposed design.

The proposed design uses all the existing functionality and gives it a single object in the kernel to control it rather than a dozen different ones. It's not a fundamental change in design to how the containers themselves work.

Ahh, well I stand corrected.