The first world can't be a new setting because this was destroyed or fragmented, but maybe one of the planes is very close to the original piece.
The poem of the "Elegy of the first world" says the humanoids, created by the deities, weren't there when it was created. The humanoids and deities are from a "no-first world".
Of course the giants can tell a different story.
WotC will have to show something about "our dinosaurs(+ prehistoric beasts) are different" to avoid others to sell their own dinosaurs toys.
It shouldn't be only based in Vikings, Celts and North-Europeans but also in other tribal cultures from other places. When I was a little child and the Far West still was popular the native Northamericans are awesome. To use this as source of inspiration shouldn't be reported as disrespectful cultural appropiation but as a homage or tribute.
Could gnomes use "speak with animals" to tame giant badgers to face giants and megafaun?
Maybe the arcane magic caused some "magic pollution" with an effect as ashes-snow, and now they have to hunt the preys who can eat the mutant flora. Something like the survival videogame "Scavengers".
* The future "Vecna's Book of Vile Darkness" could tell something about the dark domains Cavitius-Tovag, but adding vashars (evil humans) and jerrens (very evil halflings).