This week saw the announcement that IPv4 address space from ARIN was completely exhausted.
If you now require IP addresses for public facing servers you have three choices:
1) Subnet your existing IPv4 space and use Network Address Translation with Port Address Translation. This is likely to be a considerable undertaking when you also account for the subsequent DNS changes
2) Apply for IPv6 space, update your entire infrastructure (routers, switches, load balancers etc). Significant capex with potential for increased support costs.
3) Move your origin to a cloud provider with IPv6 already in place
The good news is that any request received from an IPv6 user to the Akamai platform will be translated at the edge and sent forward to your origin over IPv4. While this doesn't allow you to add more servers it does mean you don't have to update your origin to IPv6 just yet (unless you need more publicly available IP's).
Akamai has been tracking IPv6 usage for years now, have a look at the growth of IPv6 at IPv6 Traffic Volume and there is an interesting discussion on this with David Belson, author of Akamai's State of the Internet report. The thread is in the Akamai Community at Ask the Expert - State of the Internet Q&A Session - Q2 2015