Exactly. My contention is that you can perhaps regard the entire Bitcoin network (of full nodes) as providing RTGS services for the Bitcoin currency.

The question, then, is: "is this sufficient"? Do we believe all Bitcoin transactions would be transacted over this system (i.e. over the blockchain) in the future or will we see aggregators akin to DNSs?

I see the work of Mike Hearn and others on micropayment channels as innovative examples of what a DNS for Bitcoin might look like.