+1 for this one. With all the problems I've encountered over the years trying to get SIP to work through a firewall, there would definitely be situations where this could come in handy.
Although, I will also say that IAX2 isn't the ultimate solution in all cases. I actually have a SIP trunk between two Asterisk boxes that works well in every way, but if I try to substitute it with an IAX2 trunk I get all kinds of audio issues (sounds like missing packets or something). But the weird part is, I can run an IAX2 trunk between either of those systems and a third system and I have no problems at all. It's only when I try to use IAX2 between those two particular systems that I have a problem.
The other issue with IAX2 is that I don't think it can do reinvites (feel free to correct me if I'm wrong about that), so all your traffic has to flow through the server. But still, in a situation where you absolutely cannot get SIP to work because of a NAT firewall situation (particularly when you're trying to set up an adapter for a non-techie at a remote location, and they're trying to do something dumb like run the connection through two NAT routers), IAX can get the job done.
I know that Atcom devices (at least some of them) support IAX2, so it must be possible to include it in this type of device. The only thing I would wonder is how much additional memory the code would consume, and whether the OBi devices have that much to spare (without compromising other features).
An alternative would be to include OpenVPN support (an internal OpenVPN client) - as long as you had an OpenVPN server on your Asterisk box, that would give you the single port connections through firewalls and encryption, while still using sip internally. But that might be harder for the system administrator to set up, and I don't know which approach would use fewer resources on the device, but I suspect that IAX2 support would use less than an internal OpenVPN client (then again, that's just a wild guess on my part).