For certain, it will not work if one partner wants to cruise and the other to race. They will have very opposing attitudes. I do have a bro-in-law who shares his boat with another skipper. They are both cruisers, so can agree on the kit and improvements needed for that role. They sort out their "rental" periods quite easily. They do have a pretty good "will and testament" on how to dispose of the boat when the time comes.
Have you looked into the Moorings method as an alternative?