Very interesting debate! One that shouldn't be exclusive to RPT HCAOC.
In my company we are operating an aircraft that falls in to Transport Category and requires a HCAOC but we are almost exclusively operating under 'Airwork'. This changes the ballpark quite drastically as an FO looking for an upgrade has no real hindrances in the regs.
He/she doesn't require an ATPL in full if the aircraft is strictly operated under 'Airwork' ie no pax carrying. This also helps in the area of building command, as provided he/she has a command endorsement on type they can quite legally fly from the LHS (ICUS) with a C&T Captain until they have the required time/experience.
So the only restrictions really placed on an F/O looking for an upgrade are those outlined in the company's AOC and those placed on the company by our primary client. As we know the above are usually able to be palpitated to suit the company's needs.
Would the command time on type, multi-command, night hours etc ever really need to be altered? Probaly not as our operation really needs Captains (and FOs for that matter) that can think 'outside the square', so generally speaking 'more is better' and a Captain under training won't be let loose until they and the C&T Captain are completely comfortable.