What would be nice would be if we changed the semantics a bit and made it 16+48+64 where the first 16 of the dest+source could be
re-assembled
into the destination ASN for the packet and the remaining 48 identified a particular subnet globally with 64 for the host. Unfortunately, that ship has probably sailed.
On the other hand, it probably would have been easier (and more widely adopted already) to simply go to an "internet of internets" model where you break the planet up into 32-bit regions, each with their own 32-bit "internets" and just use what amounts to IPIP tunneling between them and enlarge the standard MTU from 1500 to accommodate that without further packet fragmentation. And speaking of changing MTU, is there any reason why private exchanges shouldn't support jumbo frames? Is there any reason nowadays that things that are ethernet end to end can't be MTU 9000 instead of 1500? It certainly would improve performance and reduce the packets/sec and increase performance on latent links. Why are we still using 1500 MTU when peering? Is there any gear at peering points that DOESN'T support jumbo frames these days?