They won't throw something too big so close to E3. This will mostly be an Arms+Splatoon trailer, and mabe an indie announcement.
Possibly other stuff? Don't set yourself up for disappointment. This is not even called a Nintendo Direct, it's just a straight up Arms Direct, it's not gonna have anything else besides the one trailer for Splatoon.
I could see them possibly talk a bit about SF2 and Disgaea 5 as well.. but other than that, I dont expect much else than the stated.
Nope, it's specifically an ARMS direct, much like the Pokémon Direct and the Splatoon Direct the only game they'll talk about will be ARMS excluding the Splatoon 2 trailer they specifically mentioned...