I like the idea of measuring each and every class-A-sized block
against some standard separately, since a lot of the class-C space has
been allocated to regional registries this way and it inconveniences
those places which have done the best the least. I'm less attached to
the number 1200 in particular, but I do think an explicit target should
be chosen which represents both a tractable limit to design big routers for
and which allows the implementation of efficient address allocation strategie
which won't have to be tighened over time. I do note that 1200 is
close to the threatened /18 address filter, but this is mostly accidental.
I'd much rather see each space filled with /14's and /20's, and even
an occasional /23 or /25, as appropriate and as long as the filled block
was only 1200 (or N, for some well-defined N) routes, rather than
picking an arbitrary, one-size-fits-all filter limit. The latter is
a sign of failure.
So, perhaps we should just look at the total amount of IP address space
advertised by a provider in its routing advertisements, then divide
this amount by the number of routes the provider advertises, and
see whether the resulting number meets the goal.