Earlier quoted context omitted.
In theory this could be handled by stuffing the extra 96 bits in an IP extension header. But this solves nothing because then any switch that isn’t IPv4+ aware will route packets incorrectly. Literally every single switch on the internet needs to be updated/replaced before you could start generating IPv4+ traffic otherwise the one outlier will send your IPv4+ packets off to Uzbekistan. OR Maybe you don’t use those 96…
Couple things: 1) Instead of stuffing the extra 96 bits in an extension, you stuff all 128 in the extension and use a reserved unrouted address in the v4 header field. Devices with no clue will just drop those packets. 2) Pedantically, switches are layer 2 devices. Some some of them act as routers also, but only routing is relevant.
I'm struggling to see how this would improve anything over what v6 did though.