Hypothetically speaking, if they were to include dark pokemon, technically they would not have to include the fact that they gain no experience and just make them act like regular pokemon with a different color.
I will also say with the way the shiny market is going eventually they will fall way down in price same with lucky eggs, so I think we should start a new topic about ways to fix that first then discuss about dark pokemon even though it has been debated to death. There will also be some exceptions to that like the rare to encounter and catch pokemon, like chansey.
Nebula and Fabray please stop fighting over something complete unrelated to the thread.