Thomas Brand makes a good point when it comes to the naming convention of OS X as it approaches what would be 10.10:
Mac OS X, now OS X, was never a sequential continuation of the classic Mac OS, ending in Mac OS 9. It has always been its own operating system. Its own “brand.”
I doubt there will ever be a Mac OS 11. Apple hasn’t used a numbered versioning system to publically describe their operating systems in years.
Adobe may still internally refer to Photoshop as version 12.2.3 or whatever, but to consumers it’s now just Photoshop CC. Their move to subscription-based software makes version differenatiation redundant.
The same applies to OS X now that it will always be a free upgrade. I’d be surprised if future versions of OS X still refer to version numbers within their updates and don’t just call them all “Update”. Sure, stick the version number in the release notes but most of us don’t really need to know.
All we need to know is that if the App Store has a red badge, there’s an update available.