wording quibbles:
Addresses needed for other purposes (e.g. additional services provided to the members) should be assigned by upstream ISPs.
s/assigned by upstream ISPs/acquired through other appropriate means/ could be that the ix operator could qualify for normally allocated space all by themselves.
- a /48 in most cases - a /64 if it is known that there will only be one subnet (basically following the IAB recommendation)
i suspect the 'most cases' is the /64, a single exchange mesh, and that the multiple interconnected meshes, which whould need the /48, is a rare case.
The RIRs should warn the IXP that it is strongly discouraged to announce the addresses and that they will likely not to be globally routable.
the ix does not annouce mesh address. isps on the mesh may. so i would say the rirs should warn the ixp that isps usually do not announce mesh space to their peers, so that the ix space allocated under this policy is likely not to be visible globally. randy