Don’t worry, Arc is not that daft to start working on another game while the first one isn’t done.
But yeah, future game concepts exist.
CK is planned to be a trilogy. Although the game right after this one won’t be the “CK 2”.
Either way, the plan is to start tinkering on stuff once the game reaches the beta phase.
The beta phase is pretty much going to be polishing and adding the last bits of content, with the main story all finished.