I think that it will be the killer because it will be evident as it already has become, that it cannot support the throughput that is expected of it. Like when it collapsed because of ICO transactions as it could not support the amount of transactions. I do agree it will coexist alongside, but EOS imo will take a great deal of the ethereum market cap.
Just my speculation :P, thanks so much for the comment!
No problem , maybe you haven't seen this http://plasma.io/.