Randy;
BGP Route Reflector IXPs need a AS number. I'll send you a URL with a whitepaper. The BGP Route Reflector IXPs have proved to offer a low entry cost for ISPs (for those places that do not have the deep pockets to get big routers).
except that big routers are not needed for small-isp exchanges. remember, an isp participating in such an exchange has only to add the prefixes of their local peers to their routing, typically a dozen or so. there are very successful layer-two exchanges where the peers use what we think of as cpe routers, e.g. cisco 2501s. and what's nice is that this is on the right path to exchange growth.
l3 exchange ponints are a labor suck and are fragile.
Maybe. However, l2 is for telco. l2 exchange ponints are a labor suck and are fragile. The right path is l1, though, then, there is less reason to have exchange points. It will be more obvious as the peering speed between two ISPs exceeds that of a single physical interface. Masataka Ohta