[steven2012]

Impossible? That's nonsense. They could ask users for a standard race descriptor that is never shared with the hosts, and if the hosts seem to predominantly reject certain races of people, the marketplace like AirBnB could kick them out. It's actually pretty simple. It all depends on how eager the marketplaces are to solve this particular problem.

[jaredsohn]

A nice aspect of this is that it could work better than the system being replaced (tracking gets automated and centralized.)