There are a bit more than a hundred unused protocol numbers, and the options field has more than enough room to stuff some more address space into it. You'd need enough buy-in to get the protocol number accepted as valid, and could introduce better routing gradually: as long as the OG destination address knows how to send the packet on to the extended-address computer, it'll get where it's going.

The problems, and they are real, show-stopping problems, are more social than technical.