I like the pool idea. And the system could be fluid too: Say we have a best network doing the self played training games all by itself, and a new network beat it with a less than 55% winning rate, this new network would become the new point of reference but since it's not markedly stronger, both networks would be used to produce the training games. A third network appears beating the new best with a winning rate of about 51%, the point of reference would be unchanged but now we would have 3 networks producing the training games, etc. until finally a new network appears that would have a better winning rate than 55% against the current "best network", at which point it would be strong enough to deserve the privilege of producing training games all by itself for a while :)