I don't think it will really be missed much anyway. From what I've seen so far of the new quest hints/logs, the new version does a better job of telling you what the requirements are than the old version did. It really doesn't take very long to finish everything in any version of BB if you know what you're supposed to do.Apparently sharing savegames won't work in the rebuild, savegames are now encrypted. New Ren'Py "feature" to prevent malware injection.
It's when you have things like give Alice a pussy massage on the couch 13 times without using candies without knowing that's the requirement that it can take forever. Why would I not use the candies unless I know about that requirement?
BTW that's just a made up example but there are definitely similar quests where it doesn't really tell you exactly what you're supposed to do in previous versions so I could flail away for weeks or months without making any progress because I didn't know what I was supposed to do.
I always just start over from the beginning when a game like this releases a new version. It's sandbox games like Master of Raana where I would be somewhat irked if my save game from a previous version didn't work.