When making calls to the gateway on a service that has rate limits, it would be nice if the HTTP Response Headers would contain the following:
headerLimit: The limit being applied to the service
headerRemaining: How many requests remain before the limit is reached.
headerReset: The number of seconds until the limit is reset.

This functionality is part of APIMan and is described by the following:
http://www.apiman.io/latest/user-guide.html#_rate_limiting_policy

A related issue is https://issues.jboss.org/browse/THREESCALE-121, but the intent of this Issue is clearly identify what should be in the headers.