What switching and/or service characteristics would you require such that an exchange point would be desirable (e.g., media types, switch fabric, route servers, multicast services, SLAs, ..)?

Kind of depends on what you want out of your exchange and who your target marrket(s) are. Factor in budgets, (financial, space, environmental...) and you should have winnowed down the conceivable to the likely. Enjoy. --bill