While not necessarily Linux-specific, Io Interactive who made HITMAN (which Feral Interactive ported to Linux) have confirmed they're working on another.
Conarium looks absolutely fantastic! A chilling Lovecraftian horror with some impressive visuals and it's still coming to Linux. Seems it might be quite soon too.
Pillars of Eternity: Definitive Edition has been announced for release on November 15th, bringing all current content as well as a new DLC into one package.
Heard of Zero-K? It's an open source RTS that uses the Spring RTS Engine and it's actually pretty good. They're going to release it on Steam, with a campaign currently under development.
Remember Vendetta - Curse of Raven's Cry? The game that originally released as Raven's Cry, then it was removed from Steam and eventually it returned. It's been a bit of a whirlwind and now the problems continue.
Natural Selection 2 has gone 64bit with the removal of 32bit support officially now. On top of that, they've made steps to make the flamethrower a more viable weapon.
Human: Fall Flat is a game I briefly looked over a while ago and it really was amusing, now even more so. This silly physics-based puzzle game now has 8 player online support.