I can see the attraction if you fancy 4 days on a limited service mini cruise to avoid riding through Europe to get there. But no magician or show girls. You would need to have spare time to do it or the shipping and flight is, in reality, quicker.
If retired, why not if you like watching the sea. That bit I get, I'm occasionally tempted to cross an ocean on a cargo vessel.
The return trip could be a bit busy unless port security is rather good. Can you imagine how this possible new route is being celebrated throughout northern Africa? Make people smugglers work much simpler. Could be a rather higher than normal meat content in crates of fruit and veg.
For those that aren't aware of the concept
https://www.cargoshipvoyages.com/
Max is 12 passengers, above that they'd need proper medical facilities. Eat with the officers, drink their cheap gin, wander round the ship. And if it's the right kind of boat, get your bike on board. And accept their timing and delays. Quite a few folk have used them on rtw trips to get Africa to South America. Might work to Morocco if the service starts.
€100 per day is a rough estimate of cost.