Remember these aren't nameservers that serve 5 domains, figure tens of thousands. Perhaps I am not being clear. Reloads, even a HUP, cause named, even the new version, to pause for a while before being able to serve requests again.
That will change in 8.1.2++, btw. "ndc" will use a socket, not signals.
All the relevant nameservers for the domains would have to be reloaded 300 times a day in this case. It isn't good if named stops responding that often because it slows access to the web sites domains by inserting a dropped DNS query timeout every time the reloading server is queried (50% or 33% depending on 2 or 3 nameservers. If the reload takes 30 seconds then reloading 300 times == each nameserver is down for 150 minutes a day. Not good.
Not bad, either. This is why we have slave servers.
Or do you suggest delaying client domain name registrations 24 hours?
I always put a zone up on the master before I send in the registration. If the slaves take a day or so to catch up I can live with that. -- Paul Vixie <paul@vix.com>