The business model seems clearer when offering filtering as a service to downstream networks, the effects are narrowly scoped, and members have control over the traffic they accept from the exchange, e.g. I don't want to accept NTP traffic to any destination that exceeds 1Gbit/s, or is sourced from an NTP server on my blacklist. Giving policy control to the downstream allows them to protect their networks and make business decisions about how they want to prioritize services and customers when resources are constrained.
Would exchange members pay for this type of control?
Speaking only for myself: No. The L2 IXes I connect to should use their resources for packet switching, not filtering. Way too many things that could go wrong if we go down the filtering path... Steinar Haug, AS 2116