That's cool and all, but end-user edge routers are absolutely going to have to be updated to handle "IPv4x". Why? Because the entire point of IPvNext is to address address space exhaustion, their ISP will stop giving them IPv4 addresses.
This means that the ISP is also going to have to update significant parts of their systems to handle "IPv4x" packets, because they're going to have to handle customer site address management. The only thing that doesn't have to change is the easiest part of the system to get changed... the core routers and associated infrastructure.
No. The router in your home would need to support IPv4x, or you would get no Internet connection. Why? Because IPv4x extends the address space "under" each IPv4 address -thus- competing with it for space. ISPs in areas with serious address pressure sure as fuck aren't going to be giving you IPv4 addresses anymore.
As I mentioned, similarly, ISPs will need to update their systems to handle IPv4x, because they are -at minimum- going to be doing IPv4x address management for their customers. They're probably going to -themselves- be working from IPv4x allocations. Maybe each ISP gets knocked down from several v4 /16s or maybe a couple of /20s to a handful of v4 /32s to carve up for v4x customer sites.
Your scheme has the adoption problems of IPv6, but even worse because it relies on reclaiming and repurposing IPv4 address space that's currently in use.
Is that really the easy bit to change? ISPs spend years trialling new hardware and software in their core. You go through numerous cheapo home routers over the lifetime of one of their chassis. You'll use whatever non-name box they send you, and you'll accept their regular OTA updates too, else you're on your own.
When you're adding support for a new Internet address protocol that's widely agreed to be the new one, it absolutely is. Compared to what end-users get, ISPs buy very high quality gear. The rate of gear change may be lower than at end-user sites but because they're paying far, far more for the equipment, it's very likely to have support for the new addressing protocol.
Consumer gear is often cheap-as-possible garbage that has had as little effort put into it as possible. [0] I know that long after 2012, you could find consumer-grade networking equipment that did not support (or actively broke) IPv6. [1] And how often do we hear complaints of "my ISP-provided router is just unreliable trash, I hate it", or stories of people saving lots of money by refusing to rent their edge router from their ISP? The equipment ISPs give you can also be bottom-of-the-barrel crap that folks actively avoid using. [2]
So, yeah, the stuff at the very edge is often bottom-of-the-barrel trash and is often infrequently updated. That's why it's harder to update the equipment at edge than the equipment in the core. It is way more expensive to update the core stuff, but it's always getting updated, and you're paying enough to get much better quality than the stuff at the edge.
[0] OpenWRT is so, so popular for a reason, after all.
[1] This was true even for "prosumer" gear. I know that even in the mid 2010s, Ubiquiti's UniFi APs broke IPv6 for attached clients if you were using VLANs. So, yeah, not even SOHO gear is expensive enough to ensure that this stuff gets done right.
[2] You do have something of a point in the implied claim that ISPs will update their customer rental hardware with IPv6 support once they start providing IPv6 to their customer. But. Way back when I was so foolish as to rent my cable modem, I learned that I'd been getting a small fraction of the speed available to me for years because my cable modem was significantly out of date. It required a lucky realization during a support call to get that update done. So, equipment upgrades sometimes totally fall through the cracks even with major ISPs.
I entirely disagree. Due to a combination of ISPs sticking with what they know and refusing to update (because of the huge time/cost in validating it), and vendors minimising their workloads/risk exposure and only updating what they "have to". The vendors have a lot of power here and these big new protocols are just more work.
In addition, smaller ISPs have virtually no say in what software/features they get. They can ask all they want, they have little power. It takes a big customer to move the needle and get new features into these expensive boxes. It really only happens when there's another vendor offering something new, and therefore a business requirement to maintain feature parity else lose big-customer revenue. So yeh, if a new protocol magically becomes standard, only then would anyone bother implementing and supporting it.
I think it's much easier to update consumer edge equipment. The ISP dictates all aspects of this relationship, the boxes are cheap, and just plug and play. They're relatively simple and easy to validate for 99% of usecases. If your internet stops working (because you didn't get the new hw/sw), they ship you a replacement, 2 days later it's fixed.
But I will just say, and slightly off topic of this thread, the lack of multiple extension headers in this proposed protocol instantly makes it more attractive to implement compared to v6.
