Hmm, in Discord are currently other discussions, so I post some of my civ ideas here ;-).
Grigori:
I still feel civs without religion missing something in the game, two important things are the commerce thing, what causes them to have less culture, oney income and units and the missing fun aspect. I like the Illian concept as they have their own white hand cult, bound to their culture and nature. Imho Grigori could have something like that as well. As Cassiel is an angel and want his ppl to be more self-determined a true religion or persona cult or worship to gods would not fit to them. Also Cassiel does not seem to be vain, so he would not like ppl see him as a god or emperor. Also he doesn ´t like Gods or mighty beasts that want to rule the world, like the dragons.
So there could be some kind of "told traditions" for the Grigori that replace a relgion or cult, called "dragon lore" or "dragon tales" that could be spread for Grigori only, the replacement for the temple could be some building like "adventurer Guild" that gives build uniots for example the dragonkiller promotion and maybe some + rate for adventurer spawn and some commerce. The unique Building for that could be a building called "Dragonbane" for example.
Another idea would be to rename their champions into Dragonslayer, because that ´s what they are with their dragonkiller promotion.
I know religions are on the to do list, so maybe the ideas may have some place ;-)
Sidar:
I think they feel a bit lost, in FFH they were my favourite civ with their ability to create big persons from level 6+ units, I would like to see them in this role again.
Also their sidar withdrawn life should be more present. I got some ideas about a created fog in their territory what makes this area invisible to other civs, barbs etc until they enter the fog. Making moves in fog could have a chance to occur fear by the unit so it can ´t move there for one turn, or runs back. Also the fog could be scary for bhaal units so they would not enter it, making moves in fog for enemy units could cause spectres to appear like the wood in leave religion. Sidar Workers (and other units?) could be unvisible as long as they are in sidar fog area. Fog would be OP to have all that points, but some might fit into the game maybe ,-).