This is exactly why widespread adoption of IPv6 would make everyone more productive. Why doesn't every Vagrant box have an IPv6 address that you can expose by opening up firewall rules? Well, aside from ISP's being slow and developers not spending the 40 minutes necessary to set IPA tunnel, VirtualBox does not support IPv6 addresses on bridged interfaces if the host interface is a wireless card. Sad day all around.
Edit: in fact I wonder if instead of building yet another IPv4 traversal tool, new applications that require P2P connectivity should actually start building it as an IPv6-in-something tunnel. There are plenty of ways to do this including AYIYA which while not fantastic would actually work really well here.
Several reasons. First, you are likely behind a NAT. Sure, you can share your Vagrant box with people in your office, but you can't share them if you are working remotely. This has actually bitten me on my team (I work remotely) where I needed to debug a Puppet issue on a coworker's VM and had to try to ssh to his box. What a pain.
Second, port forwarding is fun and all, but why bother when you can do things properly and directly. Your host machine can still control everything and you won't need to do anything manual. All the manipulations that are required can still be hidden behind the simple `vagrant share` command. You can even combine this with a dynamic DNS entry so that you could share not just an IP address but a simple name.
Third, it would be less effort do support this, than to maintain yet another NAT traversal service.\
Fourth, this would speed up adoption of IPv6, something we will all benefit from in the long run.
Edit: in fact I wonder if instead of building yet another IPv4 traversal tool, new applications that require P2P connectivity should actually start building it as an IPv6-in-something tunnel. There are plenty of ways to do this including AYIYA which while not fantastic would actually work really well here.