That still doesn't explain why Industrious was chosen to replace it, as opposed to some other trait. How would Summoner/Charismatic sound?
Quite nice. (Not saying overpowered, perhaps, I don't know.) Industrious isn't bad though, they can get catacomb liberalis up quicker, and/or the great library (now with expanded pedia entry), there's a few other good ones for them like the compass (for Rites or Elegy), prophecy, soul forge, mokka cauldron, infernal grimoire.
Sheaim probably don't benefit from quick forges as much, since smelting + is less useful for them, but they do have a slightly better chance to build wonders or buildings in general, getting no-build units from time to time.
I think Kael chose Industrius because he sees Sheaim as a bit of a builder civ (in FfH, that's relative, of course) or at least late game civ which would be more likely to appreciate wonders. Nothing wrong with charismatic, either, of course, but I don't know if it makes sense on Os-Gabella.
I never found it all that convincing to begin with. ... I don't think the Sheaim will really need such a boost in my modmod.
I don't think Killer Clowns was being specific to your modmod, though. And of course, if you remove Keelyn, then there are no summoners that might out shine the Sheaim with the new .33 changes.