'Hey Siri' may come to iMac Pro with rumored inclusion of A10 Fusion co-processor
The iMac Pro may have an A10 Fusion processor running it's own iOS, called BridgeOS, to handle some functions -- notably 'Hey Siri'.

Guilherme Rambo and Stephen Troughton-Smith have been exploring macOS and have found 'Hey Siri' functionality in the code base with support for multiple user accounts, just as macOS has long supported user switching.
If the accounts are correct, It looks as though the ARM coprocessor takes over the boot process, security, and the FaceTime camera. It also appears that the inclusion of the A10 Fusion allows the iMac Pro to accept the voice command 'Hey Siri' rather than requiring the click in macOS on the Siri icon or keystroke to prompt Siri.
This doesn't mean necessarily that Siri will understand multiple users speaking while logged into one macOS user account. But, it may mean that if a user has multiple accounts on a Mac, they should be able to fast user switch between them and have the iMac Pro recognize 'Hey Siri' for each of them.
It is unclear if this functionality will need a coprocessor like the A10 Fusion to be implemented in other machines.

Guilherme Rambo and Stephen Troughton-Smith have been exploring macOS and have found 'Hey Siri' functionality in the code base with support for multiple user accounts, just as macOS has long supported user switching.
Looks like the iMac Pro's ARM coprocessor is arm64 Seems to handle the macOS boot & security process, as expected; iMac Pro lets Apple experiment with tighter control without the rest of the userbase freaking out. More info & download here: https://t.co/wmbNeVSEZX
-- Steve Troughton-Smith (@stroughtonsmith)
If the accounts are correct, It looks as though the ARM coprocessor takes over the boot process, security, and the FaceTime camera. It also appears that the inclusion of the A10 Fusion allows the iMac Pro to accept the voice command 'Hey Siri' rather than requiring the click in macOS on the Siri icon or keystroke to prompt Siri.
The "Hey Siri" setup on macOS is identical to the one on iOS, but it's implemented with regular AppKit, there's no magical UIKit port or UXKit being used pic.twitter.com/lhuga3dA7y
-- Guilherme Rambo (@_inside)
"Hey Siri" on macOS depends on the presence of a BridgeOS device (A10 coprocessor).
-- Guilherme Rambo (@_inside)
"Hey Siri" enrollment model from my testing yesterday was stored in ~/Library/VoiceTrigger/SAT. Means it's going to support multiple users.
-- Guilherme Rambo (@_inside)
This doesn't mean necessarily that Siri will understand multiple users speaking while logged into one macOS user account. But, it may mean that if a user has multiple accounts on a Mac, they should be able to fast user switch between them and have the iMac Pro recognize 'Hey Siri' for each of them.
It is unclear if this functionality will need a coprocessor like the A10 Fusion to be implemented in other machines.
Comments
2) I'm curious why the 'B' is being capitalized when all other Apple OSes have the first letter lowercase.
3) A10 seems like overkill for the stated functionality, and with FaceTime mentioned I hope that this means the iMac Pro will also include Face ID.
4) Is this still launching next month?
Apple could be working towards direct running of iOS apps on OS X for development or plain ol' operation. Your Mac could become your iPad or your phone... just another iOS device, while still being a Mac.
At the same time, Apple could be testing how well the ARM runs pro-style apps or OSX. If the A10 chip is handling the boot process, then the next step is booting to the OS of choice, be it OSX, Windows, or (dun dun dunnnn...) iOS.
Remember that Apple was running OSX on intel for FIVE YEARS before they ANNOUNCED the switch to Intel. We could have ARM-based Macs in that time or less from now.
It sounds nuts. N-V-T-S, nuts. But it is plausible.
I think it would be cool to see the A10 or A11 in the next MacBook and/or MacBook Pro along side the Intel CPU. It could run the OS doing basic things and then when power is really needed it kicks in the Intel CPU. That would quite a feat of engineering though. There's a lot of software engineering that needs to take place to make something like that work reliably.
2) Laziness is outright denying the utility of a technology and denigrating anyone that uses it because you can't see how it can be useful to you.
3) You've completely ignored those who have visual and motor disables that may find an always-on digital voice assistant very helpful. But, you know, they're just lazy¡
Until now, there was pretty big concern about macOS, which is a much more open operating system compared to iOS, having any access to home automation, including critical home security devices like smart locks. By offloading this to a secure core, they get rid of that risk and can remove any chance for 3rd party access as well.
This would greatly increase security on Macs.
Obviously, it would make it very difficult to create a Hackintosh.
Only with its own custom chips can Apple insure security in essentially the generic Intel computer guts of every Mac.
This will give Apple the great option of including Face ID in every Apple Device - Macs, AppleTV, iPhones, iPads, etc.
Additionally, Siri and voice recognition can be offloaded onto the A11 Bionic so that Macs can run faster while simultaneously handling voice and other duties.
Intel Chips historically have been SO SLOW it has been maddening. Realize that by limiting consumer computers to 4 core chips, Intel chips have not progressed in speed for the past DECADE. Unbelievable.