1. What do you mean by there's "no actual changes to the estate itself"? `landuse=` is about the use. The use has changed from being uninhabited to inhabited. 
2. That's untrue. Abandonment without demolition is still `=brownfield` , as with many such polluted industries in reality in the common language. 
3. I don't see what's "painfully obvious". This can be described by `abandoned:landuse=residential` , and there are still `building=apartments` inside. 