You may have heard it already: We are running out of IPv4 addresses. In the US the official pools are empty (late 2015) - you can only get returns. In Europe we are close. At the same moment IPv6 is being rolled out by all providers.
As IPv4 addresses are now a scarce resource it is increasingly difficult to get one. I remember that when I set up a new server some years ago I got an extra block of 8 addresses from the datacenter without problems (and for free). This is no longer the case. You only get single extra IPv4 addresses, and the price is that you have to write begging letters, and if you don't have a good-enough reason, such requests will be refused. Some months ago I was successful when I had a routing problem, because you can only resolve that with extra addresses. Running a docker container is definitely not good enough.
These are our times.
So, it all means we have to do the switch now. There will be now more and more services that are only available via IPv6, in particular those that are run by small businesses who don't have the money for a workaround (like becoming a member of a regional Internet registry, or buying companies that still have addresses - we'll see that sooner or later), or even run privately.
The assumption that every service on the Internet will be accessible via IPv4 for some time is certainly wrong. Although the client side is hit more by the scarceness there is also a problem on the server side.
For gitlab.camlcity.org I ran into the problem that the ssh port of the machine was already taken. Gitlab is wrapped in a docker container, and has its own sshd. Because of this gitssh.camlcity.org is so far only reachable via IPv6.
So, what does this mean?
If you try to clone a repository via ssh (e.g. "git clone email@example.com:something") and get an error that there is no route to the host, you don't have IPv6 yet.
The better solution is to get IPv6. Go for it! Often, this is only a matter of unlocking it in the router.
If your provider doesn't have IPv6 yet, the alternative is to get it from elsewhere:
There are IPv6 tunnel providers (sixxs.net, gogo6.net, tunnelbroker.net). Best if you want to connect your home or SOHO network. Many router models allow it to configure tunnel protocols.
Roadwarriors: If you already have machines that are reachable via IPv6 and you only want to connect your laptop, one option is to use openvpn with a default route for IPv6.
The IPv6 world is simpler than the IPv4 world
Because every machine has now public addresses, there is no NAT anymore. This makes it much simpler to connect machines ("oh, box A is in 192.168.16.* and box B in 192.168.4.* and cannot talk to each other" - or even worse, both boxes are in separate networks using the /same/ subnet...).
There are so many addresses
Even a home router typically gets at least an /80 subnet. That means 2^48 addresses... every dust particle could get its own address. IPv6 is unavoidable if you want to run servers on your own and escape from the platform Internet where companies say what you can do and what not.
Professional reasons to switch
As a developer you should be able to test your own software against IPv6. Remember, it will be the standard very soon.
The global IPv6 network will be more reliable, because the routing tables are much smaller. There were already IPv4 outages because routing tables overflowed (even in large models there is only space for a couple of million entries). Also, IPv4 latencies are already higher because of this.