Regarding ideas / suggestions for an independent mini-mod, why not create a faction or two that are not too common in the existing mods currently available? If you're willing to create the units from scratch and have enough ideas for faction unit rosters, then that should keep you more than busy for a while. Here's a few faction examples (for RTW unless otherwise stated):
  • Illyrians
  • Etruscans
  • Samnites
  • Moors (for BI)
  • Boii
  • Sarmatians
  • Chinese (obviously for larger maps)
  • Saka
  • Alani

I'm sure there are many more you've thought of yourself, what do you think?