Originally, the Ignition schema did not support setting kernel arguments and lacked a kernelArguments field. To work around this, the MachineConfig schema got its own kernelArguments field, but it has different semantics to the Ignition v3.4 kernelArguments field: The Ignition v3.4 version explicitly declares two subfields for shouldExist / shouldNotExist. This means that the Ignition v3.4 schema is very explicit about what kernel arguments should be set and which ones should not be set. By comparison, the MachineConfig's kernelArguments field implies that a given kernel argument should not be set if it is not in the list.

For the sake of consistency, we should determine how to handle the Ignition v3.4 kernelArguments field. Presently, we ignore it. Instead, we could do one or more of the following:

1. Explicitly ignore the Ignition v3.4 field by degrading the MachineConfigPool whenever the the Ignition v3.4 field is set.
2. Support adding kernel arguments by combining and deduplicating the MachineConfig kernelArguments field and the Ignition v3.4 kernelArguments.shouldExist fields.
3. Support removing kernel arguments by setting the Ignition v3.4 kernelArguments.shouldNotExist field. Removing a kernel argument from the MachineConfig kernelArguments field would get that kernel argument added to the Ignition v3.4 {{kernelArguments.shouldNotExist }}list.
4. Completely remove the MachineConfig kernelArguments field in favor of the Ignition v3.4 kernelArguments field.