To be honest I wouldn’t know if it is(n’t) on a Mac or a Windows machine, I’m on Linux and know my way around
I run 4 different RawTherapee versions; 1 for my own personal stuff and 3 for testing (latest self build development, stable 5.8 and the latest appimage).
What all 4 have in common is a shared directory (/data/Images/Shared/Color/profiles) that, among other things, holds a directory called output (readable/writeable by 2 normal users).
I point to this location using Preferences → Colour Management → Directory containing colour profiles. I copied all the profiles that I use to this directory and it also holds the monitor calibration profiles created by DisplayCal.
You can only set one base output profile in the preferences section. Being forced to have the monitor profiles in the same directory, and thus showing up as an output profile that I can choose in the Colour management tab, bothers me to be honest. Strictly speaking all of them are output profiles, but output to monitor or file (or arguably printer) are rather different things.
That’s a rather good idea. If at all possible try to leave the default behaviour in tact for the default profiles. You do not want a user to inadvertently delete those.
It should be for the ones that are added by user, the default ones that come with RawTherapee should be protected (see my previous remark).
Anyway: I fully agree with what it is you are proposing/working on.