My most desired feature on Geni is for there to be a button to see how spouses are related, not via their spousal connection, but another relational path. And in general, for Geni to show an array list of numerous possible relational paths between people, instead of what it deems to be the optimal or shortest one.
I'm considering making a project "Spouses who are Cousins" containing couples who are third cousins or closer, but some may find it an offensive project.