The ARM9-loader has added a new keyX with keyslot 0x16 that is generated on hard-boot. The ARM9 binary is now encrypted with this key. In order to decrypt it, you'll need arm9hax on firm > 9.4, or some form of bootromhax.
We will not be able to support emunand 9.5 or higher for a while on the New 3DS. This is only an issue for the New 3DS, the old 3DS and 2DS will never have this issue