I think this should be simple to implement.
I frequently watch shows with subtitles and if I skip (ie. Shift+Right Arrow or clicking through the video), most of the time the skips will skip the timecode where the subtitle gets called leaving audio with no subtitle forcing the user to skip to the beginning of the audio segment so the timecode can pull the lines subtitle up.
Can VLC call the last subtitle in the case where a user is skipping through the video? I think it would make sense to check and call any subs a few seconds (maybe 5-10s?) before the skipped to time.
ie. user skips to 5:00 in a video. VLC checks the active subtitle file from 4:50-5:00 for the last subtitle line and displays that. User sees 5:00 video and most recent sub from 4:50-5:00.