My prediction is we will see a 4.6 with a mini tier. And that's where we confront Omega. There is not a chance in hell Sephiroth is relegated to chump fight status over Omega. Square wouldn't even allow it considering how immensely popular he and FFVII.

As for what bosses we may see.

v9s: Dark Nation, Midgar Zolom, Lost Number, Bottomswell
v10s: Proud Cloud
v11s: Jenova
v12s: Sephiroth and Safer Sephiroth (Savage)

The weapons could be used, though I feel those will be held off. At least Ruby and Emerald. Granted, Ozma was a super boss and wound up in a 24-man. So mayhaps the weapons do make an appearance even if they wind up being easy.