I really wonder why by this time we don't seriously consider an experiment with a centrifuge creating an artificial gravity on ISS. One would thought medical experiments like that are an important part of ISS mission. It does conflicts with some other research topics, which is the main argument for why it's not yet done, but by now it could be done without disturbing micro-gravity too much - there are options - and the topic itself is important enough so the arguments to contrary are wearing thin.