I’m just writing this down so that I can go and tell you „Told you so“ in a year or two. 🙂
I predict that there will never be a „OS XI“ or „OS 11“ from Apple. „OS X“ is a brand that has gained a pretty good reputation over the last decade. They won’t chance the number in front of the comma, but they might go and make some geeks and nerds jump out of their windows by naming a release OS X 10.10 (which, in a decimal system, would be the same as 10.1 which was already released in late 2001 („Puma“). Subsequent releases would then be named 10.11, 10.12 etc.
Or they drop the version numbering entirely and just go with animals. They didn’t announce their next release, 10.7, as „OS X 10.7“ but, if I remember correctly, solely as „OS X Lion“.
Of course, all of the above only applies if they don’t drop the „OS X“ part and just go with „iOS“ for all their devices instead. 🙂