Nobody cares that your app is written in Rails of NodeJS. People care that it works and does what matters to them. IPv4 is doomed to not work at some point so we "tech nerds" have to care and do something about it.
> IPv6 is used by nobody
From the top of my mind, many of the french ISPs have IPv6 ready on the customer side, a radio button click away, while some are even on by default. I can readily assume that today, every worthwhile machine connected to a LAN supports at least IPv6 local scope. Also, every single Mac out there uses an IPv6 VPN (over IPwhatever) when (at least) Back to my Mac is active (ifconfig utun0).
> in five years it will still be nowhere
Unless you settle for impractical definitions of "nowhere" as "not ubiquitous", it is definitely there already. IPv6 does solve real problems today, locally and globally.