Yes, it's primarily a code cleanliness issue. Part of what I'm wanting to do with it is reduce the amount of code needed to create a plugin to an absolute minimum - I think that once mbarcode gets into extras, you'll have a LOT of people creating plugins; it's just to much fun to play with! :-) Regarding the ISBN plugin, I've requested commit access on the project. As soon as that is approved, I'll commit the plugin.