I have several dating sites that use a white label platform. They are easy to start because they make use of a database of millions of members on a variety of sites.
These members often identify their religious preferences when filling out their profile, so if you want the site to be limited to a certain religion, you just have to limit the membership criteria to the portion of the database that identifies themselves with that religion. I know that there is at least one JW site that uses the same white label platform.
I have thought about setting up a JW or XJW site. An XJW dating site would be difficult because there is no selection criteria for former members of religions. A strictly JW site would also be problematic because there is no way to provide the security that devout JWs want in a dating site. I know there have been numerous complaints from JWs who are upset when they are contacted by people that they view as undesirable or not righteous enough. I wouldn't use that niche because complaints would be inevitable and I could lose my account and my other sites.
However, it wouldn't be too difficult for someone else to set up a site with the realization that they could eventually lose their account. It could be marketed towards JWs that are somewhat liberal or are fading or no longer believe. Of course many of the profiles would come from other sites where they have different expectations. It could be a lot of fun for someone who enjoys causing mischief or has a sincere interest in helping the portion of JWs who don't believe to find like minded individuals.
If anybody wants to try something like that, I would be pleased to provide some technical assistance. You wouldn't need hosting, but you would need a good domain name. I would also recommend privacy for the domain name to reduce possible harassment from devout JWs.