If I may interject? I saw the film, and one, I kinda like the idea of the wife taking the form of the first reject logo. Two, Egon can't be a cyborg, because they don't have the tech for that. Besides, the Ghostbusters are physicists, not robotics experts. Third, if Egon WERE to return it would be as a benevolent specter, who want to help the girls out.
One scrapped version had Egon in perfect living condition. The story is currently being rewritten to fit the reboot's canon better.
Just trust me. If Egon is gonna be anything, he should be at the very least, a SPECTER.
The rewritten version will be slightly different. No mentions of the original characters for this one. They're getting their own story soon.
Ahh. Okay. Well, perhaps maybe a cameo by Louis Tully then?