Some of the ones I thought of, most of those have probably been suggested already but still.
  • Resizable nameplates.
  • HUD layout preview mode (fills up stuff like party list, buffs, debuffs, etc so you can see how that element would look when filled up).
  • Split up the parameters bar or give us more layouts for it such as HP above MP, MP above HP, MP on the left of HP.
  • Shields appear on your own HP bar and not just party list's