The mediation center would be great for several reasons, both for players as well as for the GOSU business - at the same time, it comes with a lot of challenges. Setting it up requires a lot of work (technically but not only that, I need to "design" how it`s supposed to work, etc.). And then it will also require additional time and energy to maintain it once it`s up and running.
I think you are doing pretty well already. Adding the mediation service will probably increase the number of users on your website. But you have to be ready to handle some shitty, angry players who will start blaming your service if you cannot satisfy them. Look at the holy darkness. This guy is doing everything for the players and the casinos without getting paid, but at the end of the day, some people call him out because they are not satisfied.
I believe you will have to face a similar situation and handle these people, too, if you enter into mediation services. But overall, it's a good decision to increase the business size. Considering how reputable Holydarkness is, you may consider a big position for him in your company.