How much item level we need for the new content?

[Sieben79]

Gearing up to i380 isn't hard as such. Just tedious and/or expensive.

Judging from the early parts of Stormblood and Heavensward, I expect the first ShB dungeon to drop i390 or i400 gear - depending on what level the dungeon is.
I also expect the early quests in ShB to give us i385 gear before we end up in any dungeon, so better gear than that will certainly not be needed going into ShB.

If they won't add an ilev requirement, then the first dungeon will be ilevel 1 But fun aside, it will drop 390 for sure, because Sirensong dropped 260 items (like 260 shire gear) if they do the same formula in Stormblood.