The ship wouldn't necessarily be out of danger. A series with a hospital ship could be set during say, a Cardassian-Tholian war, and the Federation could be neutral and providing medical aid to both sides. There could be a secondary setting aboard a Cardassian warship serving as escort. I just threw that out as an idea. As much as I would like a TOS/TNG exploration type series, I think that after the hundreds of episodes already done, a new series in that format would just end up rehashing old stories - no matter what century or universe.