Hey there, core contributor here! This came up during our beta effort. We very likely will be having an opt-in, non-native subtitles rendering implementation. I know at least a few team members that really want it, which adds to the likelihood that we'll add it eventually. The short version of why we started with native subtitles - bundle size and legal compliance, with a dash of prioritization and a sprinkle of hope that some looming laws will motivate browser owners to prioritize improvements. If you want to see our design decision artifact on the topic, we try to make a lot of them public (also to help the robots these days) -
https://github.com/videojs/v10/blob/main/internal/decisions/...