It would be more accurate to say that a Lizardman style was playable in every SC game until 6 like how a Korean sword user was in every game until 5 (which unfortunately that trend continues into 6).
Lizardman really should be free, but he'd probably be the next DLC character if he wasn't since it seems similar to the case with Tira that they said there wasn't enough time / money to put in base game. This is definitely supported with the NPC lizardman style being an incomplete moveset, but...
It more or less seems like they ran out of money or time to complete Aeon and left a somewhat generic lizardman SC2 style moveset in the game on NPCs until they'd complete Aeon as a DLC character using his SC3 / SC4 moveset.
Edit: Just watched that mod video, they even have SC3 / SC4 taunt on it.
The 1Ps in 4 in general across both male and female were terrible. Hilde being an exception. Setsuka and Mitsurugi are the only other designs I didn't find terrible or meh on 1P.
It seems more likely he'll be DLC, they have at least two axe skins, why go to the effort of porting or making more than 1 weapon if it's just going to be for NPCs? They'll probably correct the NPCs to the proper moveset if they released him as DLC.
Thought he was going to be in the middle slot. if that is real then that last slot will be either (above random) will either be an unlockable character or Tira then.