I'm guessing this won't ever be fixed because there's a brand new (incompatible with older versions) captioning workflow coming in PPro. Except that it doesn't currently work - at all. I can add a caption, and while the video is playing in PPro, it displays correctly. But as soon as I stop playback, it vanishes. And when I export video, it vanishes too. (And I'm using open captions).
The Beta captioning is very early and not ready for real work.
BUT it will import .srt (not sure what other caption formats) AND the captions are available as Graphics text.
If I turn off Mercury/hardware acceleration, it kind of works, with lots of bugs and weirdness. But I did actally manage to create some captions and export it!
Thanks for reporting. As you noted, you can export burned in. FYI, they have not yet added the ability to export a sidecar (e.g. .srt) from the new captions.