Building a single point of compromise has no advantages over this and many disadvantages beyond just security.
Think if you had a DB with financials (credit cards and such) in a isolated DMZ with SSH inbound/outbound blocked
How can you dump the DB and copy it off if all the traffic was "proxied" through this?? It's not like you can scp a tarball anywhere.
You can't forward ports and expose the DB outside of the DMZ either.
And it doesn't take admins to setup auditing or disable forwarding, you have physically disabled it.
I got to say I don't understand the single point of compromise thing. A single point of failure is a bad, but the less points of compromise the better. You identify your critical systems, you protect your critical systems. Spreading things out doesn't make you more secure.
Here is an old white paper on some things to think about SSH in your infrastructure.
http://www.sans.org/reading-room/whitepapers/vpns/security-i...
Your right in saying this is an unproven application!