Just to flesh this response out a little bit - I've asked Meraki tech support and specifically IKEv2 support is available in MX Wired 15.12 and above. They have also said that for IKEv2 to work would require adding a back end feature. I assume this means manually activating something in the specific MX cloud account so perhaps the configuration options are visible. I'm assuming that we will need to get them on the phone to get this firmware applied and IKEv2 features activated. The usual caveats surrounding the fact this is very early Beta firmware also apply - you'd be brave to run this in a production environment.
We have a client using Azure to host Microsoft Navision. They have 3 sites utilising an MX84 at the head office and two MX64s at the remote sites. Currently the MX84 connects to Azure using an IKEv1 non-meraki peer which works perfectly for that site, but as is well documented the problem we have is that the non-peer route isn't advertised to the neighbouring MX64s - so no one at the two remote sites can access Navision over the Meraki Auto-VPN links and you can't have multiple IKEv1 connections to Azure.
Not wanting to spend money an a vMX100 which would only be used to terminate the VPN we've worked around it till now using the Client VPN feature - users at the two remote sites that need access to Navision simply "dial in" to the MX84. Of course that does make the two MX64s somewhat redundant for those users!
So yes, we've been waiting patiently for this feature too and I think it should be a source of embarrassment that its taken this long to implement it when cheaper less functional firewalls in the Cisco range have had it for a long time. Cisco Meraki is shown as "Not Compatible" when it comes to the list of site to site Azure VPN Gateway devices on Microsofts website - equally embarrassing I feel given the target market for these devices.
You can't help but feel this has been a commercial decision to force people into buying the vMX100.
Anyway there is finally light at the end of the tunnel it seems - lets see how quickly MX 15.x is rolled into release candidate status and IKEv2 is finally a standard feature.