Just like today, it is likely that most client will support your new address, but ISPs won't route them for you.
Hardware is important - fast routers can't do work in the CPU (and it was even worse in the mid 90's when this started), they need special hardware assistance.
Or, it’s in the most-significant place, meaning every new ipv40 IP is in a block that will be a black hole to any old routers, or they just forward it to the (wrong) address that you get from dropping the first octet.
Not to mention it’s still not software-compatible (it doesn’t fit in 32 bits, all system calls would have to change, etc.)
That all seems significantly worse than IPv6 which already works just fine today.
Black hole for old routers. You run the software overlay until you can run the hardware.
I wrote a linux kernel module and an node/relay daemon that runs on every host.
There is a (0.)0.0.0.0 dedicated LAN space that auto-assign IPs. I called it the standard LAN party :) No more 10.0/192.168/etc Gateway always has .1 -- sensible defaults.
Also 0-255. Adds 255 IPv4 internets of address space. Billions and Billions of addresses are more than moar than enough.
Maybe one day I'll put on a fireproof suit and post it here for fun and see how much flame I get.
My prototype/thought experiment is called IPv40 a 40bit extension to IPv4.
IPv40 addresses are carried over Legacy networks using the IPv4 Options Field (Type 35)
Legacy routers ignore Option 35 and route based on the 32-bit destination (effectively forcing traffic to "Space 0". IPv40-aware routers parse Option 35 to switch Universes.
This works right now but as a software overlay not in hardware.
Just my programming/thought experiment which was pretty fun.
When solutions are pushed top down like IPv6 my spider sense tingles -- what problem is it solving? the answers are NOT 'to address address space limitations of IPv4' that is the marketing and if you challenge it you will be met with ad hominen attacks and emotional manipulations.