I'm so glad this forum has been started, and I've learned from reading the posts here. In some ways, it seems to me that this forum's greatest contribution could be that it can become a place for the ongoing project of understanding what interstitial fiction might mean.
I see two possible cleavages in interpretation. There may be some who may be interested in a specific borderzone between two genres, say fantasy and multicultural fiction, just for example. Any of these borderzones could become genres of their own in time, like what has happened with say paranormal romance or urban fantasy.
Others may be interested in borderzones in themselves, in the idea of writing between different kinds of borders, whatever they may be. When one zone becones genre, they may be inclined to move to another because it is writing in a state of liminality, rather than the specific elements of any two or more genres that interests them.
I should maybe say that I don't think there is anything wrong with either approach, or with the idea of plural approaches.