Realistically, you should sell it while it's valuable. Take a look at IPv6 adoption. I know, I know, "IPv6 will never be here blah blah blah", so the naysayers say, but look at what Google is getting now, for instance:

https://www.google.com/intl/en/ipv6/statistics.html

We're counting down the years before IPv6 will become the major protocol, after which, IPv4 addresses will slowly start to loose value.

"But it's only FAANG, noone else has IPv6!" Just not the case anymore. But even if, most people don't care about anything else anyway. I have a friend who helps to operate a university dorm network. Allegedly, he once removed an IPv4 address by mistake from one student's computer. He only heard about it half a year later, when the student casually mentioned that only Google, Facebook and other big sites seem to work. Apparently, if Google, Facebook, and the School's website works, it's acceptable to most (which is sad for different reasons, but that's not my point).

Anyway, that's still at least a few years away though, you can have some fun with it for now :)