Star Trek: The Next Generation almost had another alien onboard the Enterprise with Lt. Commander Geordi La Forge.
Star Trek: The Next Generation executive producer Jeri Taylor, in the bookThe Fifty-Year Mission: The Next 25 Years by Mark A. Altman and Edward Gross, [via CBR.com} spoke about the original idea of Geordi being an alien. Supposedly, Geordi's mother had been impregnated by an alien, and Taylor thought it was a good idea.
" "He was going to discover that his father was not who he thought he was, and his mother had an almost Rosemary’s Baby–kind of thing and had been impregnated by an alien. As a result, Geordi was actually half alien and now, at his present age, his people were coming back to get him. I thought that would have given Geordi’s character a lot of elaboration.""- Jeri Taylor
But making Geordi an alien would have been anything but good. Not only would it have stripped away part of his humanity, but it could have changed how he interacted with the crew of the Enterprise and how he saw himself. Though Taylor might think it would have been good for Geordi's character, LeVar Burton didn't need any help bringing the Enterprise's chief engineer to a place where he stood out among the crowd.
Making Geordi La Forge an alien might have presented some interesting concepts, but LeVar Burton did that all by himself.
Geordi went through human emotions when he lost his mother. He experienced real pain and trauma that probably would have been different as an alien. And what type of alien did the producers believe would have been best for Geordi? An Andorian? A Tellarite? Klingon? Or a new specis altogether? And how would it have been revealed after seeing Geordi as a human?
The TNG writers did a fabulous job with Burton's character with the exception of his love life. (They really dropped the ball there.) And there was already an android and a full-blooded alien (Worf) and a half-blooded alien (Counselor Troi) aboard the Enterprise. It might have been cool to see Geordi alienized for an episode or two like when Captain Picard was assimilated or Troi was turned into a Romulan, but overall, Geordi was best as a human with human flaws.