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.
<p><a href="http://knitmeapony.tumblr.com/post/104790747494/i-was-looking-up-the-etymology-for-succubus-and" class="tumblr_blog">knitmeapony</a>:</p><blockquote><p>rachelbearenson:</p><blockquote>
<p><a href="http://tchy.tumblr.com/post/104785640994" class="tumblr_blog">tchy</a>:</p>
<blockquote><p><a class="tumblr_blog" href="http://fuckyeahmonsterenbies.tumblr.com/post/104760689717/i-was-looking-up-the-etymology-for-succubus-and">fuckyeahmonsterenbies</a>:</p>
<blockquote><p>Hey this is a really interesting concept to consider! Also takes away the sexism that incu/succubus connotate. Thanks,</p>
<p>I’ve been using “concubus” for years—that one’s “to lie with.” Same root as “concubine,” actually.</p>
<p><a href="https://tumblr.com/tagged/so-if-we-take-%27concubus%27-to-be-the-gender-neutral-term-for-incubus%2Fsuccubus">#so if we take ‘concubus’ to be the gender-neutral term for incubus/succubus</a><a href="https://tumblr.com/tagged/does-that-make-a-procubus-an-ace-demon-that-kills-people-by-cuddling-them">#does that make a procubus an ace demon that kills people by cuddling them</a></p>
<p>IT SURE AS HELL DOES NOW</p>