I love Shared Cockpit too with the A320.
I would be totally fine if only one gets the time. I think Pilot Monitoring should get the time, as he talks to the ATC. We normally swap the rules after each flight, so both would get enough hours.
Do you think Shared Cockpit will be available at the beginning? - so both might log on but only one will be visible on the radar? That would be a amazing step for everyone flying Shared Cockpit, to get a even more realistic feeling, thanks Andrew