Therefore Chancellorsville or Shiloh may be the best choice for a one off new release. However maybe the best way forward would be to look not at a single battle but at a campaign. Last year I released a TC2M Vicksburg OOB pack and to date this has been the most downloaded mods I have done also the Atlanta campaign and Shermans March to the sea pack got significant attention. Another way of increasing interest would be to maybe add new gameplay options like Gunboats and fortifications for seiges (although I appreciate that would mean a heavy investment in additional development).
My final idea would be to look at releasing a map editor and a scenario creator - I'd certainly pay this and I suspect others would do as well.
Just a few idea's - Hell whatever you release I'll buy it - I'm a loyal fan and devotee

Zeke