Maybe the fact that they are less standard could mean less ease to service?
Watches can easily be stored in safes for investment sadly... 
On my side, it is not at the top of my wish list but I would love a JLC Atmos with moon phase. The idea of having an "eternal" movement giving forever the time with the additional poetry of the moonphase fascinates me.
As you say, this would be similar to an art piece inside your house that only visitors could enjoy. A different approach compared to wristwatches.
Best,
E.