Prior to WWDC21 in June, Apple posted a job posting for a homeOS-related position. At the time, after the press started covering this unreleased operating system, the job announcement was updated and replaced with links to tvOS and homePod.
And now, a few months later, Apple is once again announcing a vacancy for a senior iOS UI engineer on the Apple Music team to work with homeOS.
Apple currently has two central home operating systems: audioOS for HomePod and tvOS for Apple TV. audioOS is based on tvOS, but the two systems are understandably different in their capabilities. The "homeOS" operating system, as part of a long-term strategy and future product plans, could help better unify the company's home offerings into a single operating system.
Given that "homeOS" has reappeared in yet another job posting, it's safe to assume that Apple has already thought about it, but just hasn't made it public yet. Alternatively, "homeOS" may only be an internal code name and may never become a software platform for public use.