IPv6 usage is steadily increasing, currently hovering at 10% globally, and 23% in the US. [1]
This is driven partially by mobile deployments, partially by some ISPs rolling out support. Note, that the IPv4 address exhaustion referred to in the media is IANA-level; top-level exhaustion occurred on 31 January 2011 [2]. Also from there:
* Four of the five RIRs have exhausted allocation of all the blocks they have not reserved for IPv6 transition; this occurred on 15 April 2011 for the Asia-Pacific, on 14 September 2012 for Europe, on 10 June 2014 for Latin America and the Caribbean, and on 24 September 2015 for North America.
None of this impacts end-users, as ISPs have large reserves of non-used IPv4 addresses; and there are multiple mitigation strategies for post-exhaustion periods.
Also note, that even if all IPv4 address would be in public use currently, we still wouldn't "migrate" to IPV6 at-once: seeing how there are roughly ~25 billion Internet-connected devices (and 3.17 billion users) using it currently, migration can't take place overnight. Also note, that "pure ipv6" devices currently would be heavily disadvantaged: the majority of sites & services can't be accessed via ipv6 yet.
A probable migration pathway might be ramping up allocation of IPv6; as usage increases, servers will roll out support for it; which might hit a tipping point (similar to the current "HTTPS for everything") sometime around the 40-50% penetration rate. Once that occurs, ipv6-only users will no longer be disadvantaged; that, along with increasing price-points for dedicated ipv4 address might shift ISPs to start deploying ipv6-only, and use relays to access ipv4 services.
However, even under these conditions, servers will almost certainly will provide v4 access points, for reasons of maximum compatibility, and low cost (relative to all dev, deployment, domain, etc costs).
In conclusion, you can rest safely knowing that the code you wrote will be in use for a long time to come.
[1] https://www.google.com/intl/en/ipv6/statistics.html
[2] https://en.wikipedia.org/wiki/IPv4_address_exhaustion