If you give one half of the station twice the mass of the other, you can test out living in lunar gravity and Mars gravity at the same time. Maybe only one of those will turn out to be enough to stop bone loss. Maybe neither one. It would be better to know that before building a base.

The zipline would be trickier to make work, then. Probably you have a gadget that walks up the tether, and then you flip around and it walks down to the other end.