> Today these machines can send millions of emails, portscan servers or participate in DDOS attacks and the user has very little if any noticeable performance hit.

Unless the downstream vs upstream economics of the Internet backbone become severely asymmetric, technological advances that lower the price of bandwidth will benefit everyone equally. Once you get down to the subscriber line level (e.g. ADSL) you do see asymmetries but biased towards downstream, which speaks against your argument.