Evolution:
Each agent is represented by a function; for concreteness let it be a real function of some relevant subset of previous turns. If the return value on a given turn is positive, the agent cooperates, else it defects. The function is represented as a tree; each node is a function with a fixed number of parameters (zero parameters = constant). Mutations are realised as cutting random branches and replacing them by constants. Sexual reproduction would take two functions and swap some branches. Population dynamics would be basically the same as in the last tournament.
Variable match length:
I would simply make up a number N which I will not tell anyone before the game starts. Then, each match would be preceded by generating a random real number x between 0 and 1, and the match length would be set to exp(xN) rounded up to integers, or something similar.
This sounds interesting, however the longer I think about it, the less I'm in support of it.
Regarding match length, I think the main issue here is not that it is variable, but that it is unknown to the agents. This will lead to a tournament of nice strategies first exterminating all non-nice strategies, then always cooperating with each other. This won't change even if you can simulate your opponents, because the smartest way to play against TFT is still TFT (CooperateBot). If you take away the whole concept of parasites, I don't see much of interest left....
Last year, there was a lot of interest in the IPD tournament with people asking for regular events of this sort and developing new strategies (like Afterparty) within hours after the results were published and also expressing interest in re-running the tournament with new rules that allowed for submitted strategies to evolve or read their opponent's source code. I noticed that many of the submitted strategies performed poorly because of a lack of understanding of the underlying mechanics, so I wrote a comprehensive article on IPD math that sparked some interesting comments.
And then the whole thing was never spoken of again.
So now I'd like to know: How many LWers would commit to competing in another tournament of this kind, and would someone be interested in hosting it?