I love the fact that bookmarks can be put into subfolders with this app. However, the current procedure for re-sorting seems a bit tedious. I have to unmark a verse from the general folder, switch to the subfolder, and then re-mark the verse while in that folder.

I was wondering if it would be possible to add the ability to drag & drop a bookmark into an existing folder? Or, could a 'move to folder' option could be added?

I think you can already do this. Find the bookmark in the bookmark screen then tap edit at the top. Now just tap the bookmark you want to move and select the new folder for it.