I would hardly call it a "major drawback" given no-one else has shown the slightest interest out of the thousand+ users of this plugin.
You have workarounds - you could always remove/add the book to the list again and find it that way. To my mind arranging the order of a list is a case of looking your way down it and rearranging as you go to put your next few you want to read at the top. Perhaps one day I might feel motivated to allow alternate sorting, but right now it is not on my TODO list.
As for putting the order in a custom column, indeed it would complicate things. Particularly since the user could completely screw things up by typing into that column.