I’m also interested in this feature. I have a 7 days trip split into 7 mlts each with subtitles that I was hoping I could export in one go.
The external workaround I found is to export the 7 projects individually and use ffmpeg’s concat feature to merge them together (fast and lossless). You need to use “-map 0” argument and ffmpeg will also merge the subtitles together along with video and audio.
The only downside I found so far is the occasional cracking/pop sound in between the individual projects (this can be fixed by adding fade in/out audio at every start/end of the project).