It's funny because I was wondering the same thing after recently rewatching that episode... I was thinking that it would have to look like Roger. My logic for this is that since the egg was created inside of him, with no real help from any one else, he just "passed" it along to Steve, who then passed it on to Betsy. So having said that, I don't see how it could have human characteristics. I think this will come back in a future episode & Stan will find out because the baby will be brought into the CIA. (Who knows, maybe the child will eat a burrito & poop out gold w/ encrusted jewels...?) :)