Should've clarified: this was in the context of IPv4...
To be honest, I'm not sure what the appropriate equivalent would be in IPv6 (/128 or /64? Arguments can be made for both I suppose).
There have been discussions of this sort made over the years. A good place to start would be the old (well, maybe not that old) 6Net site where there's a list of publications called 'Deliverables'. The info is buried in other, but amongst other things it contains deployment scenarios as well as cookbooks decumenting IPv6 deigns and roll-outs, and what they learned from it all. Lot's to read, but good info nonetheless:
vixie had a fun discussion about anycast and dns... something about him
being sad/sorry about making everyone have to carry a /24 for f-root
Whether it's a /24 for f-root or a /20 doesn't really make a difference- it's a routing table entry either way- and why waste addresses.
I once suggested that due to the odd nature of the root name server addresses in the DNS protocol (namely, that they must be hardwired into every caching resolver out there and thus, are somewhat difficult to change), the IETF/IAB should designate a bunch of /32s as "root server addresses" as DNS protocol parameters. ISPs could then explicitly permit those /32s.
However, the folks I mentioned this to (some root server operators) felt this would be inappropriate.