There is not only the multihoming issue but also the PI address issue. Even if any ISP would run his network very competently and there were no outages we would face the ISP switching issue. Again we would end up with either PI addresses announced by the ISP or BGP by the customer. With either the DFZ continues to grow. There is just no way around it.
The way around it is to stop growing the DFZ routing table by the size of the Prefixes. If customers could have PI addreses and the DFZ routing table was based, instead, on ASNs in such a way that customers could use their upstream's ASNs and not need their own, then, provider switch would be a change to the PI->ASN mapping and not affect the DFZ table at all. Owen -- If it wasn't crypto-signed, it probably didn't come from me.