I am not sure about the base idea, but isn't the ipv10 (i.e. protocol number 10) going to cause problems? Aren't hosts expected to choose the highest protocol

I am not sure about the base idea, but isn't the ipv10 (i.e. protocol number 10) going to cause problems? Aren't hosts expected to choose the highest protocol number they understand? So basically this forever kills (protocol) ipv6 and replaces it with ipv6+ipv4, which is never going to fly (because the "underlying" ipv4 is sunsetting and hopefully gone within a decade)...