The IPv4 Unicast Extensions Project has lofty goals and many of them, like this particular one, seem overly lofty.
Some of space they are after, like 240/4, was always just "reserved" and you won't find as much resistance against it as reserved things are intended for exactly this kind of proposal. They just need to convince folks it's reasonably likely to be the best use of the space, overriding any significant unauthorized usage or alternative proposals as being less valid a use case, and it could be reasonably done. Real world implementation of the change might be a different story but they could at least get consensus that it's the intended use going forward.
Other spaces like 127/8 were actually assigned for use in the wild not just reserved for future use and despite 127.0.0.1 being most common address the others in the assigned space were definitely actually in use as well past the /16 they wish to preserve. This is especially in more networking infra focused contexts which are the things that would need to change most universally for this proposal to work. It's unlikely such a breaking standards change would get any consensus i.e. IMO that proposal is likely to never leave draft status.
David Täht, who was one of the authors of that draft, even holds regrets on the 127/8 proposal as it has caused the project to receive a lot of negative focus https://github.com/schoen/unicast-extensions/issues/16 and they have since let that draft proposal expire which is why your link is to an archived copy.