Kiwidude, many demand kitchen-sink plugins for any number of product. End users always have varied needs that they're happily to express. If followed to its final form, the world would only need a single program that did everything.
Calibre is a solid product with an exceptional feature set. It has a defined database that others can access with their own applications
I have been through the design process with clients and have seen those change over time. Those were modest and well thought out changes. There are gotchas along the route but sometimes change is beyond an option.
There are departments that even had additional need for "their" fields. Those always seemed best served to me with linkage from a secondary database and apps to service those needs.
But, all of that was definable. Here, it is a Chinese menu with unlimited ordering from column a and column b. That makes for a maintenance and code nightmare. We always compromise code standards over time even with modest change requirements. It is the rare event when that is 100% avoided.
You want to provide all those nifty extra fields? Great. Link to the basic db and add to the secondary all those fields -- however many thing you see a need for. It lets the original product be and preform the services intended. You'll need to code for all that rococo but what the heck, you'll have fun doing it. You can throw in a gargoyle on one of the pediments to remind you of me.
Or you could become a SAP programmer or user and really have the kitchen sink but I wouldn't wish that on anybody.