BTW, there is an ancient bug 624626 reported against libxml2, which requests proper escaping of IPv6 address with '[' and ']' and removing those when parsing URIs. Having that fixed could save us from providing a wrapper for xmlParseURI.

Don't we have to deal with systems with the broken libxml2 anyway?

*** Bug 624626 has been marked as a duplicate of this bug. ***

In POST:
http://post-office.corp.redhat.com/archives/rhvirt-patches/2012-February/msg01365.html

Verify it with libvirt-0.9.10-3.el6 and it passed.

The steps are as follows:
Prepare two machine: one client and one server
1. 
1.1 on client host
configure ipv6 global addr:
#ifconfig eth0 inet6 add 3ffe::101
1.2 on server host
configure ipv6 global addr
#ifconfig eth0 inet6 add 3ffe::102

2. 
on client host, execute remote access and issue the bellow command:
# virsh -c qemu+ssh://root@[3ffe::102]/system
root@3ffe::102's password: 
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh #

    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
Cause
    libxml2 is parsing IPv6 URIs differently than expected
Consequence
    IPv6 connections with ssh used invalid IPv6 address, connection didn't work
Fix
    Parsed addresses were fixed internally in libvirt
Result
    IPv6 connections work properly

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2012-0748.html