devs posted an update on another forum:
Your involvement in RUINER community is awesome and heart warming.
The reason why Linux was removed from the store page is that it will be coming a little bit later.
We originally planned to launch RUINER for PC, Mac and Linux at same time, but we faced some technical challenges in the later stage of the development and porting the game to consoles.
As soon as we launch the PC, PS4 and X1 versions, we’ll focus on the remaining platforms. You can expect an update in a couple of weeks.
We’re sorry if we caused confusion with the mixed messages.
To sweeten the waiting time a little, we can reveal that there will be a small surprise coming together with the RUINER Linux version.