All other things being equal - assuming that they could be - rather than investing in remodeling or modifying the main dwelling unit on a property and sometimes performing a substantial reconfiguration of the space at a corresponding large investment, adding an accessory or auxiliary dwelling unit (both called an "ADU"), transitional home, tiny home, shipping container home, granny-pod, or in-law quarters (all variations of the same theme with different names) to the backyard is a great alternative.
First, no disruption of the main dwelling is necessary. A year, two years, five years, or whatever period of time from now, that home can be sold looking exactly like it does now in terms of room sizes and configurations, door sizes, window placements, and other features - regardless of how functional they are in terms of market appeal. The home can just go on being what it is.
Second, rather than modify the main dwelling - if it is for the principal occupants of that home - they can simply relocate to the little, more efficient, compact home "out back" and use the main home for storage, cooking, bathrooms, or even as a rental property (subject to local codes).
Third, if the new, smaller residence is for relatives, nothing needs to change in the main home to accommodate them, and they will be getting a brand new setting for themselves. Both the occupants of the main dwelling and those coming to live in the auxiliary unit will be happy with their space.
Fourth, the relatives coming to live in the ADU, if that is the case, would have total independence to come and go as they desire and are able to do so without being under constant visual scrutiny of others in the household. Still, they are close enough that a lookout can be maintained for their safety and well-being.
Finally (at least for this list), when that home has served its purpose, it can have several other uses. It can house teenagers or the twenty-somethings after college, it can be a workshop or studio, it can be a man or lady cave, it can be a media center, or it can be a revenue-producing rental apartment (if that is allowed). It also can be totally removed - sold to someone else or recycled as appropriate.
This is to think creatively about aging in place solutions that do not involve remodeling of the main structure by coming up with a completely separate secondary dwelling.