Scale Limits of Multi-Domains

Howdy,

I absolutely love your plugins and service and am a raving fan of yours. I hit a big roadblock today with some esteemed colleagues of the Wordpress community. They examined the MU site I setup using your Multi-Domains plugin. I have 600 root domains and potentially tens of thousands of user created subdomains. While my install does work now, it only has about 50 domains up and running, and another 200 subdomains.

They expressed grave concerns that I won't be able to scale. To create 1,000,000 subdomains off of one domain is one issue, but to create so many user generated subdomains off of each of the 600 other root domains is another, especially the way WordPress 3.1 will handle WP MU. They expressed concern on how DNS management will be handled and if this would be a major resource drain since it has to basically emulate a DNS manager as well as a mapping tool.

Are there real world customers you are aware of who have successfully scaled not just one root domain, but hundreds, and then added thousands of subdomains to each?

They proposed an alternate root, which is basically to have the admin setup each subdomain manually on an as needed basis, and not give this instant power to the end user. Do you have any additional insight?

As always your feedback has been most appreciated.

Martin