Just Good Friends
If people in multiple dwellings don't wish to share beds and bathrooms then living space has to give. So far, the hotel room typology has received most attention. Apartments are already the size of hotel rooms and various ways of dealing with the absence of living space are being proposed.
These apartments are two or four hotel rooms joined by a shared living space. It's a co-joined suite with ownership split across two/four mortgages with rights to use the shared space in much the same way as with multi-occupancy houses.
It offers less privacy than living alone but more than does sharing a conventional two-bedroom apartment. Couples may even prefer to live this way, as might marrieds. The two-story variation has four bedrooms, bathrooms and entrances sharing a lower level living room and an upper level mezzanine.