No, there won't be an 'extra' OS.
iOS was derived from macOS (formerly Mac OS X). When Apple began developing the iPhone in 2005, Steve Jobs decided to "shrink the Mac" rather than enlarge the iPod, which led to the creation of the iPhone Operating System (iPhone OS) based on the existing Mac OS X foundation.
- Both OSs use the Unix-based open-source core named "Darwin".
- Both operating systems share the same XNU kernel (components of the Mach microkernel and FreeBSD).
- Many foundational technologies and frameworks are shared, though iOS uses Cocoa Touch (optimised for touch input) rather than the standard Cocoa used on Mac.
So, it could be Cocoa Touch on the up-coming Touch MacBook. And, the rest would be the same macOS as in other non-touch macBooks. Why waste money to create another OS, when all the technology is already available?