How about an MPEX-style solution? A well-capitalized company opens a premiere exchange, and rents a limited number of "seats" at the exchange, say 100ish seats, for some market-determined rate.

This company focuses on a few core competencies: being fast, being reliable, and being secure. Managing these three is a good bit easier with only 100 clients. The bulk of the AML, dealing with customers, etc. then rests on the shoulders of brokers, which are the companies renting the seats at the exchange, and trading on behalf of their customers.

Perhaps this is the niche Tradehill is aiming at.