Kesh said:
At that point, any of the hosts' special abilities would be lost in favor of the new form.
From the Template description:
"...It uses all of the base creatures statistics and abilities except as noted here."
"
Special Attacks: A half-illithid retains all of the special attacks of the base creature..."
"
Special Qualities: A half-illithid has all the special qualities of the base creature..."
All things considered, one would wonder why Humans are the "standard" Illithid when far more viable and potent options seem to be available through the template (they aren't even restricted by size anymore!!!).
Another thing occured to me: It refers to Humans being the only race that produces "true" Illithid, while in theory Neothelids are the "true" form obtained by these creatures, unless, of course, they were created by something with the specific intention that they grow from Humans (which eliminates the possibility of them having an empire that predates Humanity).
Oh, well, DM's call, I guess... Besides, they're not OGC, so I had to find something
nastier to replace them with anyway (which wasn't easy, but think I've just about got it).