I think a lot of us would agree that in the original game, Xen felt a little short. I was going to suggest a brand new level that focuses around the underground caverns of Xen and the natural habitats of the Antlions.
As TextFAMGUY1 (a developer) said in This post, they won’t be adding antlions to Xen. No canon changes or anything of the sort.
As far as canon goes, I think it’s safe to say that considering Xen is it’s own universe, it’s not hard to believe that Gordon just doesn’t visit any Xenian islands that are populated by antlions.
Antlions are from the same universe as the Vortigaunts, they are not native to Xen. (in fact, nothing is native to Xen)
This is confirmed in Episode 2 when one of the Vortigaunts says the following:
The Vortigaunts were forced by the Nihilanth to be slaves. Antlions just lacked the intelligence necessary to be slaves, obviously. They probably started coming to Xen (and then earth) when the Nihilanth died and shit in Xen hit the fan.
Just my 2 cents.
EDIT: Haha, didn’t know there was someone on this forum called “Vortigaunt”. Lol.
Just add some voicelines\antilon eggs in vortigaunt “homes” or something like rock paintings with antilons on them.
That would be both be cool AND canonical! I like it.