I'm Plugged Into a Robot Who's About to Kill My New BF and It's Taking A Long Time AMA
Been just sitting here listening to Ode to Joy for like 2 hours now. It was really awful, and still is. This sucks, but it's taking so fucking long...so I took out my phone. I'm fucked up, I know. But I've got time to kill ama
Well, there's this open access edited volume Anime Studies: Media-Specific Approaches to Neon Genesis Evangelion; it's not generally about that, but there might be some tidbits (and relevant to the OP, there's a chapter entitled Creating Happy Endings: Yaoi Fanworks as Audience Response to Kaworu and Shinji’s Relationship).
More relevant to your question, here's a random assortment of Google Scholar results: