someone was sharing these prototype KG screenshots and there's an interesting thing about the reaper statue (no old king look like it)
(final version)
considering that we see a lot of these giant robed figures, here's my take (please ignore Nyx's derp face); its possible that the old kings didnt exist back then, instead the grim reapers (the robed figures) had a similar role of defending the city (bond by the pact the kingdom had with Etro).
as it was stated before, the people of Insomnia believed in shinigami and the city was full of allusions to them (and it's still the case even in the final version).
the Myth mural has reapers killing daemons but the curious thing is that one of them is harming a summon, and the same is true in this picture where shiva lies on the ground with tons of spears alongside two robed winged figures, which then brings to my other point:
summons were guardians of specific nations before instead of general protectors of the planet, so i assume Niflheim, having controlled all the other nations, had the summons somehow at their disposal and thats why the reapers are depicted fighting some of them. Odin was probably Lucis summon (his name was in the datamine in the list, also death related), and Niflheim had Bahamut as their main one; would explain the emblem and this art:
here i think they just reused an old asset, but you can notice the similarities with the statue from the early Kingsglave image above to
the broken figure in Leide...
the final game and movie still has figures and art depictions of reapers
(this is exactly the same art datamined by XZero)
the statue inside the aquarium tank in the party scene of Kingsglaive is also a statue of a grim reaper (even though you can't see it) according to the
artist who worked on it; theres also
this on Nyx's room.
hard to say if they scrapped this whole deal with them entirely (the datamined Terra Battle collab event involved one) or simply toned down due to censorship but im inclined to believe the old kings kinda replaced their role in the story (giant spiritual entities asking for sacrifices?) because of the difference in the early/final KG screen.
to be honest not a bad trade if this is how it went, the kings are epic but i think the summons having allegiances to certain nations would be more interesting if my theory is true.
+Bonus
even Stella was in KG pre-production
thanks for reading my late-night ramblings lol