Even if they were good, Ronda and Shayna are both establishing themselves in their own roles. To throw more women out there with them is just Three Stooges Syndrome. One day, when they either get a lot better, or even if they were already good and just stayed that way, it could make sense. But it makes more sense to just run with things naturally and wait until it gets to that point.
I mean, what does it even mean? Who really cares about their off-air relationship? Ronda is working in her role, Shayna is working in hers. Shayna coming up and eventually feuding with Ronda makes enough sense, and their friendship can be mined for drama, but I just don't think this Horsewomen thing is the way to go at this point.