If some investigation is done that supports the use of a high rpm/small diameter module to promote health, then the question of cost and schedule becomes important. I think an early economical method might be to reuse an expendable upper stage that would otherwise burn up on reentry.
Depending on what upper stages are available to a station facility on orbit, it may be possible to use one of them to create a multipurpose centrifuge without building a dedicated module for the purpose. Even a twenty odd foot diameter centrifuge would be a volume hog in any near term space station. I suggest that a used upper stage could be fitted out in a manner similar to the wet lab concepts of back when.
I seem to remember that the wet lab concept was abandoned because of the difficulties of fitting out an ex propellant tank with a lot of complex equipment using valuable astronaut time while in microgravity. If a very simple facility is required, it just may be feasible to fit it out in an economical manner and use that upper stage that was going to burn up otherwise. With the relatively heavy engine and light tanks, it seems possible that spinning the stage end over end would put the spin center at about the intertank region for some vehicles. A spin coupler to the intertank region could connect the used stage to the microgravity station. Existing hatches (if any) from the intertank region into the tanks would serve as entry to whatever facilities were placed in the ex tanks that are now heath maintenance facilities.
One of the problems frequently mentioned is the quantity of time required for exercise in microgravity in some scenarios and motivating astronauts to do the full effort specified. Often enough the “I think two hours mandatory exercise a day is a great idea sir.” translates to “Whatever it takes to keep me on flight status, you chairborne @#$%.” One possible solution is to use the high gravity time to do things that are seriously enhanced by the presence of gravity, real or artificial. This is also a shot at compensating for the head in traction annoyance that I am suggesting for avoiding motion sickness.
Inability to take a shower in microgravity is a complaint sometimes mentioned. A shower at 2 gees with water recirculated would be a daily destination of choice for most space travelers. A good hot shower is a luxury after a hard days work that many people enjoy. That gives about 10-20 minutes a day in a gee field by choice.
A toilet in a 2 gee field would be a simpler device than the zero gee devices and most likely more desirable than the currently available arraingements. Five to fifteen minutes a day per person, again by choice.
A few minutes in a gee field might help clear out the sinuses to the point that a hot cup of coffee would taste good. Breakfast after a bathroom and shower break could be the meeting place of choice in the mornings if food can be smelled and tasted properly. Other meals likely would be eaten there for the same reason for a total of an hour or more per day per person. Eating standing up would be an acceptable trade off to people that could retire much of their required exercise time during meals.
An exercise facility would still be required in one of the tanks with possibly half an hour a day or less being acceptable if the participants are already spending a couple of hours a day or so in a gee field of substantial strength.
This is all speculation about an idea that is dependant on controlling motion sickness in a several rpm field for up to an hour at a time, and that the time in that field will produce the health benefits hoped for. If this turns out to be true, big if, then a station or Mars cycler might prefer an arrangement like this to the tether solution as the travelers will be able to transition from microgravity to a gee field and back in a minute or two whenever they feel the need. They would be able to do the things that are enhanced by microgravity and the things that are enhanced by gravity in the same ship.