You asked if they're gonna have dual wielding....but then ask if they're gonna implement the Sephiroth boss fight...I feel like people only care about Kingdom Hearts because of KH2 and that's why topics like THESE come in. Only reason. Clearly those who don't care about the lore and care more about every single flashy stuff that KH2 had clearly doesn't care about any game except KH2.
To answer your question I highly doubt an update for HARD MODE is going to just come out of the blue with dual wielding and Sephiroth's boss fight. If you want more content to come out, wait for the DLC like the rest of us. Nomura tending to Critical mode, first. The game's difficulty spike being too easy has been a big enough complaint that Nomura's tending to first.