Comment by pjf

great post! key points for me:

1. 100 IXes alone would get 56% IPv4 and 61% IPv6 prefixes, but ~14% reachability

2. little uniqueness between exchanges: not many new prefixes after the top 5

3. for outbound-heavy networks IXes are great, but to attract traffic they are not (edit: applies to automatic peering via route servers)