I just came across this and installed it. IT WORKS! I had the Nexus4 before and couldn't wait for this. I did a sideload. I renamed to Wallet2.apk myself so I could install it.
adb push Wallet2.apk /system/app
It turns out that not only is the apk rollout staged through Google Play, but activation is also staged on the server side. As a result, some users who download the app and sideload it will get an error until the rollout is at 100%. This won't affect all users, so just be aware that this issue could arise and the app will work as it should once the rollout has been completed.