I think the greatest function this editor is missing is a "CREATE NEW" option
It is useful for subtitles manipulation, but it soesn't let you to create one from scratch (to create one I always load an existent one and then edit it)
I think I wrote this somewhere before, probably in the features request post...
Maybe there are other improvements I listed... I have to check
EDIT:
Yes, there are some improvements listed in the feature request post:
http://bsplayer.com/forum/viewtopic.php?t=11112
There is one also by adicoto
Search for Subtitles Editor under PRO section ;)
With these add-ons I think BSplayer subtitles editor will become one of the best one on the market :D