Toralf Förster:
Given the numbers of https://torstatus.blutmagie.de/index.php there are about 40 Tor exits which covers 1/3 of the whole bandwidth of all exit relays. I do wonder if under-weighting the big relays in favour of many smaller relays would make it harder for an adversary to de-anonymize the traffic ?
A more diverse tor network (more relays, in more locations, and a more balanced cw-fraction across relays) would probably make it harder for an adversary which can only observe a few spots on the internet to watch most of the tor traffic. Manipulating CW values makes it certainly possible to distribute traffic more evenly but that comes with a performance impact. How bad is it really and how much are you willing to "pay" (in latency+bw) to make it how much better?
In the end its usually performance vs. anonymity properties. Bad performance results in fewer users, and smaller anonymity sets imply weaker anonymity properties.
Unfortunately there are no incentives for geo or AS diversity or even limits like "any given hoster/AS/country/operator.. is not allowed to host more than ___% of the tor network".