1: Nezarec's line "Psions, do you still revere me?" (May not be the actual voiceline from Neomuna patrols, but I remember it no better)

Yes we know Psions once worshipped him from both lore and how their helmets look. We also know that they stopped when Calus enslaved the Psions, but the helmets remained still.

Seeing how encounter 1 of RoN, Cataclysm, has Psions that need to be killed in order to have a Tormentor spawn to extend the Sweeping Terror debuff (wipe timer) is also somewhat of a link to me. It is known that Tormentors are most likely the clones of Nezarec, or from the same species as he is from.

2: similar attacks when booping runners

Nezarec uses the same attack as Psions use, when he is booping a runner if noone makes him aggro. Either the devs were lazy to implement a new attack or there's something else behind this.

3: both Psions and Nezarec have 4 fingers on hands and feet (not sure about Psions having 4 toes, as we never saw that)

Had an argument over this. Some people missaw that Psions have 4 fingers and said they have only 3.

Psion models have 4 fingers on hands, that's for sure, after having observed multiple models just for this one theory I cooked. I mean, there is a possibility of a Psion having lost a finger in some way but meh, never saw that in-game. Then again we don't know how Otzot looks like.

4: Tormentor 'language':

Been sitting around the game, trolling Tormentors sometime. And I noticed that the 'language' they speak has a few... words? (not sure how to call it) that sound similar to the occasional Psion chatter heard from enemy Psions.

Nezarec speaks whatever language the game is set to but knowing he's an ancient god, he's not a native <insert game language you are using here> speaker. If Tormentors are indeed his clones, he should be able to speak in the same language, if not, well then they are remnants of his species.

5: psychic abilities

We all know from lore (except those who DON'T read lore) that Nezarec is capable of using psychic abilities. Guess what Psions can also do. I mean, could be that the ancient Psion race received this ability from Nezarec as some sort of 'gift' from their god, but it's not confirmed. It's all just theories and findings from the game that were (mostly) never confirmed. Though, I use canon sources too, I'm not ENTIRELY sure this whole theory is true, or if Into The Light or Final Shape shows anything new or confirms a part of this theory.

Conclusion: I am heavily theorizing that Nezarec was once a Psion, OR was from the precursor race to Psions, and was transformed by the Witness when he became a Disciple. Some lore pieces hint that he was a god even before becoming a Disciple, not sure if it's canon or not.

Take everything here with a grain of salt as this is NOT the canonical origin story, just a theory based on lore and findings in the game. There are still a lot of things unconfirmed, and they might not even be the correct parts to the theory.

Also yes I'm a lore nerd.