Well, I took the plunge and purchased one of the V3 hubs. I thought I would share my experiences.
First, on the purchasing experience…I went to a local Lowe's and there was no mention of the V3 hub. There did appear to be a couple new V3 devices, but no hub. I asked one of the Lowe's employees about it and showed them the page on their website, which indicated that this store was supposed to have one in stock. After some poking around, they did find that they had two locked up in "the cage". It's interesting that there's yet to be much information provided on this device.
Now on to the transition….First off, I don't have a huge system. I'm in a rather small single story house and have 39 devices. Most of them date back to V1, with a few V2. Unfortunately, as has already been lamented in this thread, there is no automated transitioning procedure for going from V2 to V3. Per instructions, you are directed to:
1) Remove the V2 hub from system (which "removes" all devices)
2) Take screenshot of Rules and then delete them
3) Take screenshot of Scenes and then delete them
4) Pair the V3 hub
5) Pair devices to the V3 Hub
6) Add rules, scenes and schedules
They give some estimates for how much time to set aside to perform the transition. To cut to the chase, this became an all day (and night) activity for me. Most of that time being spent on a couple of main issues. I started with transitioning all the contact sensors, then motion sensors, and then various other sensors. These all went pretty smoothly, but each device did have to be reset before they could be repaired, which did take some time. Then I got to the keypads. I have three V1 keypads and one V2 keypad. The first V1 went pretty smoothly and the next two took a little more effort to get them into the pairing mode. Then I hit the V2 keypad. This one took hours! It even resulted in a call to Iris, which didn't solve the problem and required a future call-back. The device simply would not go into the pairing mode. Somehow, trying all various strange combinations and tricks, I finally got it to pair. Then there was the last major hurdle…re-pairing to GE Z-Wave switches and sockets. No matter what I did, none of the devices would pair with the new hub. It then dawned on me that these devices could have been orphaned by the removal of the V2 hub. Whether it was necessary or not, I reinstalled the V2 hub as different place and then using Z-Wave tools, systematically used the Remove Z-Wave feature to remove each of the orphaned devices. After doing this, I was then able to successfully repair them to the V3 hub. From there, I completed the transition by adding back my rules and scenes.
All the above isn't necessarily unique to the V3 hub, but the experience did lead me to some conclusions that may be helpful to others planning on making the transition. Additionally, after completing the transition, it's unclear how I'm better off, other than that I now have a talking hub like we had in V1 :). I presently DON'T have any wireless communication to the hub, due to the way it was configured. This leads into my recommendations.
First, if you want wireless capability, make sure you DO NOT connect the Ethernet port of the hub during initial set-up and DO perform the configuration from a phone app and not via the web portal. I didn't set it up in this manner, as I saw no such guidance. It turns out that if you initially use the Ethernet port (and web portal), it will use this and not enable the Bluetooth and WiFi communications. I was told this (after the fact) by Iris technical support. They stated that they could enable them remotely, but currently there's no configuration option for the user (perhaps a future capability?).
Second, based on my orphaned Z-Wave issue, I would recommend cleanly removing all your devices from the network BEFORE disabling the V2 hub. I think had I done this, I would have saved quite a bit of time.
Lastly, since you will have to reconfigure your whole system, take as many screenshots as necessary to adequately capture the WAS condition. Don't forget the schedules (not mentioned in the installation guidance), else your memory may be taxed, as was mine.
Sorry this was so longwinded, but hopefully others will benefit. Here's also hoping that the future brings new capabilities that makes transitioning from V2 to V3 worthwhile.