Wasn’t Mega Man originally called Rainbow Man?
Not exactly, from what I’ve seen. Apparently, very early on they tossed around the possibility of naming him “Rainbow Senshi Miracle Kid” but dropped that after a while. (Thanks to Joshua Savage.) There were other possible names bandied about before they settled on “Rockman,” which you can see in one of the interviews. As far as the English games go, I don’t know what other names they considered before choosing “Mega Man” once they’d decided to change the name.