and in case you are still missing it, the issue isn't about having a machine with an address in the first 32 bits talking to a machine with an address that's larger than 32 bits.
the issue is having a transition while everyone still has addresses that fit in 32 bits that would allow some machines to be on IPv4 and some machines to be on IPv6, all talking togeather, and it would only be as machines started to use addresses that didn't fit into 32 bits that there would be any incompatibility.
If this had been done, most of the systems out there would be running IPv6 now, and talking to IPv4. but since IPv6 was made completely incompatible with IPv4, running IPv6 became a significant effort rather than a transparent upgrade. As a result, almost nobody is running IPv6 except as a showpiece or hobby.