While Android 7.0 Nougat did indeed start its rollout to a number of Nexus devices yesterday - with factory images being uploaded today - that doesn't mean that everyone has access to the Google Assistant, the leaked Nexus Launcher and other goodies that are set to be coming to Nexus devices this fall. It appears that will be coming with the first update, that Google is already working on. With Nougat, Google decided to do quarterly maintenance releases, and the first one is likely going to hit around the time that the two new Nexus devices are announced. Which currently is slated for around October of this year.
What is being referred to as "MR1" should come when the new Nexus devices are announced, and should include all of the proprietary features that the Nexus devices have been rumored to be getting. It makes a bit of sense, seeing as that would be after LG unveils the LG V20 which is now confirmed to be the first smartphone to run Android 7.0 Nougat. This also means that Allo likely won't be launched until around October as well. Seeing as the Google Assistant is heavily integrated into Allo - as well as Nougat - you can't really have Allo without the Google Assistant.
The new Nexus Launcher that has shown its face a few times already, didn't ship with Nougat yesterday. And again, this is likely why. It'll likely be part of the MR1 release for Android 7.0 Nougat. Currently, there's no confirmation of any of this, but more of speculation from those that have been leaking information about the upcoming Nexus devices as well as Nougat. So it's important that everyone takes this information with a grain of salt or two. It shouldn't be long before confirmation does appear for this though.
Currently, HTC-made Nexus smartphones are slated to be coming in October. A date that has been thrown around already is October 4th. Again this isn't confirmed, just rumors, but that's around the same time that Google always unveils new Nexus smartphones, so the timing seems about right. With Google unveiling Nougat a bit earlier this year, it's thrown off everyone's schedule. In fact the update to Android 7.0 Nougat appeared almost two months earlier than usual.