n00b said:

Is there really an occasion where someone needs subtitles and the overlay for rounded corners at the same time? TESB doesn't have any burnt-in subtitles, every existing GOUT-synched language track can be added to the file and everybody speaks English anyway.

A little offtopic, but I'll hopefully be able to take care of it in one post. I don't know about this particular framing, but similar graphical frame overlays have been done for open-matte DVDs where the user could optionally apply black bars to achieve the original aspect ratio. That scenario also presented issues for people who needed subtitles.

The best way to add subtitle tracks is via graphical files, not SRT files. You are correct that the SRT files could be added without interfering with the rounded corners overlay. There are lots of reasons this is a less than ideal way to manage subtitles, though--no black borders for SDH subtitles, no subtitle shift to avoid onscreen text, lots of client subtitle rendering bugs out there, etc, etc. I imagine some subtitle files are completely unusable for most people in SRT format, and I really don't recommend using the SRT format unless you have no other choice. And, although I'm working to address this, some languages, including those spoken by nearly half the population of Earth, are not yet available in SRT format, so graphical is the only way to go there anyway.

Lastly, not everyone speaks English. Really. I get PM'ed all day from people who have friends and family who can't watch English-only preservations without either a dub or subtitles. Often, English-speakers need English subs--SDH subs, for example, and in South Asia, it's common to show English-language movies in English with English subtitles for people who have trouble with the various English accents.