So I've been debating an alternative way of doing this.  Instead of having echo be an "external" or top-level flow, that it would be an internal one, on a channel.  The coordinator switch would accept a new channel of type:echo (or type:forward) and all BODYs would be sent to the specified hashname, either externally or internally (still musing the merits each way there too).

The benefit of an external echo is that it is very lightweight, and it would be "cheap" to support as a required mechanism.  What I don't like yet is the complexity, as well as if it's revealing anything extra about the connectivity state (that isn't already visible).

It's very important to create a strong and 100% supported mechanism here, but also to keep it simple and not open to abuse... still debating the best strategy for that :)