You'd still need to upgrade and change every device. There have been transitional software that used ipv6 but allowed for ipv4 address notation. [1] Example:
::ffff:0:8.8.8.8
The huge prefixes allow for a simple hierarchical network structure and gives us room to redo the address scheme if we end up wanting to (only a portion of addresses space is currently allocated right now) without having to go through this entire upgrade the internet again.