Totally workable solution, but i have to point back at djb's argument.

If there is even a single customer that only has access to ipv6, you have to support them 4 and 6. My office, and your office will of course stay on ipv4. I'm pretty confident least one university will soon be strapped for cash, and sell of the boatload of their ipv4 space, and just give the dorms ipv6 addresses. there will be much whining and complaining, and everyone will support ipv6 the next week.