What is the current state of AAC encoding?
As I've followed the topic over the years, for a while Nero was developing an AAC encoder...then they stopped. The best last I checked was iTunes, which is still under active development. For iTunes you could either just encode through iTunes or use qaac through foobar to get true vbr encoding. The difference in size and quality seemed negligible, especially as storage costs have decreased over time.
Has anything come up since then?
xHE-AAC but it's quite niche.
"Classic" AAC looks to be complete.
Still plenty of terrible hardware LC-AAC encoders in the wild.
FDK-AAC & QAAC are the only AAC encoders I'd trust quality wise.
iTunes and its associated qaac tool remain prominent for AAC encoding.