Hi Colin,
I am using the ‘Semantic Linkbacks plugin’ but I’ve not looked at the database or what it does at all. This theme, sempress seems to handle a fair bit.
As you say a lot of trouble, but you are blazing a trail and it is one that has a map provided by the IndieWeb. I am hoping that eventually this (or something like it) will be the standard way of blogging and adding conversation to blogs. My next step is to better understand what is going on rather than just activate plugins and see what happens.