That's not actually what the current policy document says. It's actual wording is:
5.4.1. Assignment address space size
End Users are assigned an End Site assignment from their LIR or ISP. The size of the assignment is a local decision for the LIR or ISP to make, using a minimum value of a /64 (only one subnet is anticipated for the End Site).
Ok, it has changed and I did not notice it. By the way this is TERRIBLE English. Parentheses are no substitute for clear language. The size of the assignment is a local decision for the LIR to make. The minimum value of the assignment is /64 which is to be used when only one subnet is anticipated for the End Site. Of course this leaves out some important context explaining that all ordinary End Sites such as businesses and homes, should be allocated enough for multiple subnets. The overall recommendation globally, from the designers of IPv6, is to allocate a /48 to all End Sites regardless of their size, unless you are CERTAIN that there will NEVER be more than one subnet at the site. So even though RIPE policy leaves it wide open, there is still such a thing as best practice, and there is guidance from other sources. One of those sources is ARIN policy in which they suggest that it is acceptable to assign a /56 to End Sites which are homes or individual apartments. They did this because cable ISPs were concerned that allocating a /48 to every home would be too wasteful. I believe that American cable companies have to allocate IP addresses for every home that is reachable by their cable system even though many customers will use DSL or dialup or wifi Internet access from another company. It would be nice to see an IPv6 addressing best practice document that covers all these areas, whether they are RIR policy, technical or administrative issues.
So, in answer to the original question, 30m /64s is fine if that's what is needed and 30m /56s is fine if that's what is needed and 30m /48s is fine if that's what is needed. There is a presumption of subsidiarity in the policy text, putting the choice into local hands.
Seems to me that the question was not as vague as your answer implies. The writer referred to 30 million DSL, Cable modem or mobile users. If those really are 30m DSL or cable modem users, then /64 is NOT the right answer. /56 is what is needed for homes, and /48 is needed for businesses. There is no advantage to the ISP to ever allocate less than /56, except to very special sites where they are certain that there will never be more than one subnet. For example a fibre amplifier site might get a /64 or a city traffic light control station, or a kiosk on the street. This is an area where more guidance is needed complete with real-world examples to help people understand how it should work. --Michael Dillon