We have been trying to deploy IPv6 for 20 years now. This would be comparatively easier and buy us another 20 years to finish v6 deployment.

A ton of old equipment would need to be upgraded to use 240/4 for IPv4 unicast. We'd run into weird issues where it works for some people and not others. I'm not convinced. If this was done 25 years ago, maybe.

And 50% of the internet traffic is IPv6. The proposal here is to introduce a separate (arguably harder) change which would start at 0% support again. Beyond that, it'd just be a temporary fix.

Just 240/4 allowed specifically for private network use (like the 10/8 range)... that I could get behind though. This would still exclude 255.255.255.255/32 of course.

The problem is that you can't really move completely to IPv6. You actually will have to run both IPv4 and IPv6 networks indefinitely. Which isn't a lot of fun.

Now, yes. But eventually, we'll reach a tipping point where that isn't necessary. When? Your guess is as good as mine.

"You actually will have to run both IPv4 and IPv6 networks *indefinitely*."

Sure you can. You can do it today even, let alone in some unspecified number of years.