Your idea of "peak hashrate" alone is definitely something new POW coins should take a look into...this could completely eliminate the colluding problem, but I guess one could just split his mining rig to beat this.
Actually it is not fully my idea. I implemented something similar when being hired to work on an altcoin. I didn't think much of it at the time, but now realize it can help to make mining more competitive. But it is not a silver bullet and I am still pondering whether it will make much of a difference. I think it will help, but I want to see people really demanding this before I work on a pull request for Bitcoin.