That is politically impossible as most of the PoPs are run by different ISPs. It is technically possible, but futile, as the prefix won't be announced in global BGP from the PoP (as the ISP running the PoP handles routing), thus the only option would be to put up tunnels between the PoPs, which would just cause your latency to increase as there would be an extra round-trip. The "solution" could be Mobile IPv6, HIP or SHIM6 and other such protocols. ISK is only mostly a stopper from people to request too many things while actually not having anything in use and thus wasting resources. It is also a motivation for people to keep their tunnels active and working and hopefully in use. At a certain point indeed one has too much ISK for it to be useful. We are trying to come up with something that one could 'spend' it on, but we haven't found a good solution for it yet, especially as there is no real counterbalance for it.