I think we're drifting away from the original point, which is about not letting corporate marketing departments decide how the written language should work. I used Swedish as an example of a language where this is a more firm rule than English, but Swedish is certainly not alone. It just happens to be the language I know best.
But, I do find the topic of Swedish writing standard to be interesting, so I'll be happy to do my best in responding to your questions, even though I'm not formally a linguist (although I was raised among them)
With regards to your question, I'd write Ios, because it's not an acronym and I do believe that I'm not alone in this. About the version number, I find at least one case of the use of Ios 10 at Svenska Dagbladet: https://www.svd.se/apple-har-atgardat-problem-med-ios-10/om/...
However, it seems to be highly inconsistent, and this is probably caused by these organisations saving money on proof readers.
