#3. Murphy feeling guilty for hurting the Mysterio family
Murphy has to despise the man that he sees in the mirror right now. Not only is that evident by the way the man helped torture an innocent family for months, but also by all the bodies he left in his wake. This means that Murphy has a lot to atone for in the coming weeks and it could start with joining the Mysterio family.
In all honesty, Murphy's character has to feel a lot of guilt after what he did to the Mysterio family. This should drive him towards some kind of redemption storyline. Whether that manifests in joining the family to battle Rollins or otherwise remains to be seen, but the possibilities are endless with this one.
Furthermore, WWE seems to have a lot of interest in keeping this storyline going. That's why they are going to need some twists and turns along the way. If nothing else, having Murphy join the family would be a nice turn of events. It would also help showcase some of the guilt that his character might be feeling for previous actions.