By the time that qemu 1.7 will be released, enough time will have passed since qemu 1.1, which is the first version to understand version 3 images, that changing the default shouldn't hurt many people any more and the benefits of using the new format outweigh the pain.
qemu-iotests already runs with compat=1.1 by default.
8ad1898 qcow2: Change default for new images to compat=1.1
block/qcow2.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Upstream: git.qemu.org