I am considering a proposal for something of the above. A sample description is
This site is for gamblers, casino and industry professionals, and those interested in aspects of the games, workplaces and life of the casino and gambling industries.
It is related to several existing SE sites, but has a number of components that these do not address: they are not on-topic per that site's description, the expertise is not available in sufficiently supportive levels, the questions are very specific to casinos and gambling where other sites would have to generalise.
But before a proposal is even made, it needs to have a place to be proposed in. Which is most suitable for Casinos & Gambling?
It definitely has legs in all three of the above areas (Culture, Life, Recreation) and a hand resting on two more (Professional, Business - though these seem markedly less suitable than the aforementioned set).