The problem isn't a lack of research, it's lack of deployment. OS vendors aren't turning on ECN and they largely aren't enabling their new congestion control algorithms by default. Slow-start of some kind is still absolutely required, because with an initial window of 10 packets a single new connection can swamp a 5Mbit or slower link for 24ms or more, and that occurs far too often in the real world to ignore. Interactive usability is more important than shaving a few seconds off bulk downloads.

If ECN and fair queuing were generally supported on the internet at large, then senders would get quicker feedback about congestion and the negative side effects of overly-aggressive senders would be greatly reduced. Even without deployment of those throughout the network, delay based congestion control at the endpoints helps, if the sender turns it on.