Exciting news! There was an announcement today on the Kickstarter about the next expansion after TCaR:
While Pinnacle focuses on production and fulfillment of There Comes a Reckoning, Pine Box Entertainment (the design team) will be hard at work designing and play testing Too Tough To Die, Doomtown: Reloaded's next expansion!
Too Tough To Die will be bigger than There Comes a Reckoning and expands the story to Tombstone. The plan is to launch it in 2018, and feature a new way for players to jump into the game.