I love the idea of FB and RB doing a res debuff, especially if a portion of it were unresistable so it could still be effective against AVs.
Basically anything to lift FF up would be an improvement. At end game, so many melee heroes are already near maximum def/res, and bubbles do little (or less) to help. AVs shrug off knockback (and most other debuffs to be fair), so FF has a very diminished end-game role. FF is great through the mid levels, but that’s less than half of the game.
FF already has a deficit of solo-friendly powers. So anything that both helped the team and was still a benefit while soloing would be great.