I was looking up the etymology for Succubus and Incubus to find a gender neutral term, and I found your post. From what I can tell, Incubus comes from in+cubare, Latin for "to lie upon" and succubus from sub+cubare, Latin for "to lie beneath." Using this knowledge, I made the term Procubus, which should be the equivalent of "to lie beside." I thought to share it with you, in hopes that you may find it useful.
Hey this is a really interesting concept to consider! Also takes away the sexism that incu/succubus connotate. Thanks,