There's Still A Lot We Don't Know
Finally, it's important to note that the Nexus 5 Android M update is far from finished. We still have weeks to go before it's released. And in that time, we're likely going to see new features and fixes pop up. We know a lot about Android M right now but we don't know everything.
Android M Developer Preview 3 will reveal some of those new details but we expect the public release to have some features and fixes that Google didn't outline on stage at Google I/O or include in the early Android M beta. Google on Tap is probably just one of the things its holding back.
It will be important for you to keep your eyes on the Nexus 5 Android M update ahead of its release and in the weeks afte its release.