I believe problems of IPv4 are related more to IoT than end-users currently. There is not much urgency for humans to switch within ~3.7 billions of IPv4 address

I believe problems of IPv4 are related more to IoT than end-users currently. There is not much urgency for humans to switch within ~3.7 billions of IPv4 addresses unless all of humanity will suddenly decide to own a web-site with unique IP or a dedicated IP from their ISP. But there is an enormous number of devices being connected. This also brings the more important aspects of IPv6 to the front: its increased security, extensibility and performance. IPv4 is very old and wasn't designed for the modern world, it uses crutches to adapt. So the answer to your question "when will its lifespan end" depends on how fast will new IoT-devices saturate the market. It can be a few decades or a few years, only prophets know. Overall it's not a fast process but it's better be ready for the transition than not.