Like many others, I supported a userVoice entry that asked for IPv6 support in AzureAD Named Locations.
After a (very) long time without any further feedback, the latest preview now has support for IPv6 in Named locations.
The docs page isn’t updated yet, and please read the statement: Any changes made here will not appear in the old view.
You can turn on the Preview anytime in the AzureAD Admin Center:

The AzureAD Named Locations Preview (Please read the statement in the header):

Here is the IPv6 support:

That really made my day! I do use a lot of IPv6 and I have a partner, who only has IPv6 (His provider doesn’t provide an IPv4 via Dual Stack anymore).
Update:
I did a quick test, the Microsoft Graph API seems to support the new IPv6 address ranges within the Named Locations:
{ "@odata.type": "#microsoft.graph.ipNamedLocation", "id": "ab81cc2e-9cec-4608-8188-05501824cf6f", "displayName": "IPV6TEST", "modifiedDateTime": "2020-05-23T00:48:56.6479076Z", "createdDateTime": null, "isTrusted": true, "ipRanges": [ { "@odata.type": "#microsoft.graph.iPv6CidrRange", "cidrAddress": "2003:a:2651:2123::/64" }, { "@odata.type": "#microsoft.graph.iPv6CidrRange", "cidrAddress": "2003:a:2651:2100::/64" }, { "@odata.type": "#microsoft.graph.iPv6CidrRange", "cidrAddress": "2003:a:2651:2121::/64" }, { "@odata.type": "#microsoft.graph.iPv6CidrRange", "cidrAddress": "2003:a:2651:2122::/64" } ] }
So instead of #microsoft.graph.iPv4CidrRange
you just have to use #microsoft.graph.iPv6CidrRange
. That is pretty neat!