Not disagreeing with the existence of the job name in game already but that doesn't do much to prevent a Geomancer being created. Like lore behaves anyways they could just add more details to it, new revelations, different takes, w.e.
Or in other words "we can't see that person again, they're dead" SE: "hold my beer". Almost in all situations lore doesn't prevent anything from happening, at least given some new dialog, content, revelation, time passage, some change. Doesn't even have to be bad things like retcons either, like if the seams from one of the other shards started to fray into the shard with Geomancers.. causing their school of magic to go topsy tervy. Slight variation on the job, like Geoknights instead of geomancer, new hydaelyn lore that causes a change, etc, etc, etc, etc (thinking of story like technology, tvs today flying cars tomorrow, the impossible being somewhere in the future). Now SE can do whatever they want with the job.
Not saying you said that stuff can't happen, but I see people use lore way too hard a lot here lol. And I was unsure if that's what you were attempting to do, if it was just a word of caution vs "NO"- while caution is fine and true I believe the "no" would be a incorrect so long as SE had desire to make it so (lore no's is probably a pet peeve of mine since they've been proven weak in the face of player and dev desire, but people still use them like they're made of the finest iron). Like with summoners or beast tribes, both of which I've seen people be like "no way the lore says no" and then some time later it clearly didn't. If all you meant is a caution, that SE had to perhaps fiddle with things, then yeah okay lol indeed Geomancer has already been referenced (actually I think White Mage moving away from element spells and into holy spells makes me think there is a higher chance they're considering to do something with those elements later).
Given development time and thoughtful lore team we're fine with pretty much whatever players and devs want (where the importance being if it would be fun to play/provide something interesting).