I'd define true net neutrality quite simply as delivering the same performance to all traffic regardless of source or content of that traffic.

That said QoS and other more complicated traffic engineering mechanisms are widely implemented and seems kind of hard to get rid of. Google for example makes use of egress peer engineering techniques to ensure certain applications of theirs will take lower latency paths to customers, while they may shed other traffic from customer VMs in Google cloud to higher latency paths. Or we might move Skype traffic onto low latency backbone paths and give it lower latency over some other traffic that we can't identify. Does this count as non-neutral? If so, that's a really-really big deal for all the cloud providers, Microsoft, Amazon, and Google who do this.