This is very, very nice!
I do think though that if we're really honest one of the statements in this document isn't entirely accurate.
The relationship table frees the topics from imbedded links making topics more reusable and aids maintenance of links.You've stated the party line here. But for those of us who have done this for a long time will tell you all we've done is moved the headache of link maintenance from the topic to the map level. Have we freed the topic? Yes, but we've not really created an easier way to maintain the links. I liken it to sweeping the dirt under the rug. Does the room look clean? Yes, but we've just moved it somewhere else. Reltables in that way too.
In fact, after years of internal debates, we've decided it's no easier to maintain reltables vs. sticking a link in a topic itself. As long as you use keys wisely, in some cases it can be easier to have the link in the topic. Now, that's not always the case, but as is often the case in DITA, there's no one size fits all.