I like the idea of a medic. But, I would think it would be more likely for Luke's wife to have died off screen prior to the events of Ep VII. All of the protagonists thus far have lost or been without a mother. And it would solve the problem of introducing a new character that we have to believe is now "part of the family" without getting to know them. It would be very easy to say that Luke married, had kids, and then his wife died either by some illness or under mysterious circumstances that will somehow be tracked back to the big bad for the trilogy.