Yes, it does sound like it could turn into a rather large project. The code mentioned in original link does not actually monitor for any 'Events', just records some stuff before making any changes, then compares those recordings with the same objects after making all changes, to see if they still match. But attempting to record various possible aspects of a vast assortment of possible entity types within a drawing document, as it loads, in and of itself sounds almost insurmountable. Then the other half of the problem...trying to go back through that vast assortment of possible entity types to compare the various possible aspects of those entities with the previously recorded data.
I don't know if you are aware of all the possible 'Events' that are available for us to utilize in Inventor, and the extent to which we are able to extract detailed information and/or filter what we respond to or not, but there are more than what you see within the Event Triggers dialog. And when you create your own custom event handlers, you often have a lot more opportunity for higher efficiency, accuracy, and functionality. Here is a link to one of my contribution posts about creating and using your own custom event handler codes. It was written with iLogic in mind, but the same principles apply when used within AddIns and vb.net, and trying to use custom event handlers by using iLogic rules is rather 'clunky'. I don't actually have much experience with creating add-ins, due to corporate restrictions at work (no employees are allowed administrators rights on their own PCs), but understand a lot of what's required. If you could monitor for certain events to happen, you might be able to use that to know when things change, and utilize the event handler to record or edit things related to those changes, to help with a project like this. Unfortunately there aren't many drawing document specific events that I know of right now that would be useful to monitor besides retrieving model dimensions to the drawing.
Wesley Crihfield

(Not an Autodesk Employee)