For anyone reading along who needs system apps (Jeroen Dijkman) enabled, it *is* possible, you just have to tinker a little bit.
As mentioned above, you can already do it with Zero Touch (by adding the "PROVISIONING_LEAVE_ALL_SYSTEM_APPS_ENABLED" command as mentioned above in DPC Extras) and Knox Mobile Enrollment (by ticking the "Leave all system apps enabled" box).
If you're NFC'ing, then this blog from MS helps: https://blogs.technet.microsoft.com/cbernier/2018/10/15/nfc-based-android-enterprise-device-enrollment-with-microsoft-intune/ - and add the PROVISIONING_LEAVE_ALL_SYSTEM_APPS_ENABLED command.
If you're QR coding… then what I did is:
1) Go to "Corporate-owned, fully managed user devices (Preview)", save the QR code as a picture
2) Decode the QR code in an online decoder (Google/Bing has many)
3) Take the produced text, add in the PROVISIONING_LEAVE_ALL_SYSTEM_APPS_ENABLED command
4) Reencode the text to a new QR
Just to be clear the full command you want to add is:
"android.app.extra.PROVISIONING_LEAVE_ALL_SYSTEM_APPS_ENABLED": true
Worked fine for me!
It's been mentioned that MS are "working" on this with Google... but after reading the Android documentation this is a setting that needs to be enabled before Intune is managing the phone... i.e. at the QR code point... I can only assume MS will alter the Intune portal to have a checkbox to enable system apps that would then regenerate the QR code to have the right commands embedded in it... it's quite a small tweak, so I'm surprised this hasn't already been done, or information on how to manually do it passed on.