In effect the MPL holder (which includes a type rating) gets a job with a carrier that has ICUS provisions for when the F/O is the handling pilot.
The danger here is that MPL pilots will quickly start to log ICUS merely because the captain lets them handle the flying from the RH seat. This then gives a false indication of real in command under supervision. There is no shame in being a first officer as far as logging of copilot hours is concerned - although some seem to think so. My view is that before MPL pilots are permitted to legally log ICUS they should have done a minimum of 2000 hours logging as copilot time in their log books. It is absurb to have an MPL pilot logging ICUS soon after he gets a job in the RH seat when in fact he is still learning on the job to be a fully competent copilot.