Man, I knew alot of crazy things were happening when the Demon Towers were losing their connection to Goetia, but I don't know if it ever mentioned this part specifically or if it was, I didn't remember it.
https://www.reddit.com/r/grandorder/comments/ab14fl/some_of_the_unseen_events_described_to_have/
"And some Pillars like Alloces and Orobas were executed by the other Pillars for
switching sides and protecting the heroic spirits."
Now that would've been something interesting to see done. Epic of Remnant did confirm that some Demon Pillars did survive, but I don't think any of them were a Demon Pillar that fought for the Humans and Heroic Spirits. The idea of a Demon Pillar going to the human side and looking at things from their side sounds like a story with huge potential, alongside the idea of a Demon Pillar possibly becoming a Summonable Servant. It just sounds like something with alot of potential.
Also the bit that there were some Demon Pillars who just stopped fighting and just talked with some of the Heroic Spirits also sounds cool.