The question a developer is really asking is not whether wellness is fashionable. It is whether it changes the performance of the asset.
In our experience it does, but rarely through the spa line on the P and L. It shows up in positioning, in the pace of residential sales, in average length of stay, and in how long a scheme stays competitive after opening.
The durability argument
Interiors date. Orientation, section and landscape do not. A development whose wellness position lives in its architecture ages differently from one whose position lives in its furniture.
The most defensible amenity is the one a competitor would have to rebuild to match.