What brand(s)/model(s) of devices are you talking about?  Is the current Android Enterprise agent not working in all of these devices?

Were you asking about "seamless" migration from DA to DO "without"  device factory reset?

Primarily Zebra devices, yes without the user having to initiate a factory reset or entring in wireless credentials.

The devices are running Marshmallow/Nougat but upgrading to Oreo is not an option because the device agent isnt compatible

Did anyone from Soti  or Zebra tell you they are working on such migration without factory reset?  You would be lucky that you are a Zebra customer if Zebra really commits to make that happen for their devices.   Technically, skipping factory reset can be quite complicated if high security and integrity of the file/memory system need to be maintained.

I don't think that kind of seamless migration is possible or endorsed by Google.     I advise you to stop dreaming about that, as I don' t think Google will define something new to support migration of legacy implementations which differed between different EMM vendor on the market.  It's the responsibility of each EMM vendor to follow what Google define for Android Enterprise platform, not the other way round.   

Zebra is working on a DA->DO migration option but I would not hold your breath on it as there are a number of complexities as RC has outlined. For the time being, you can already use StageNow to set the SOTI agent as DO, bypassing any of the Google Setup Wizard based methods (NFC, QR, DPC identifier, ZTE) and that might be the best option to explore for the time being. I don't think you're going to have any luck coming up with a process that does not involve manually touching the devices but you may be able to unenroll on DA and then re-enroll on DO using StageNow. With that said I have only ever used the SOTI AEDO enrollment from a relatively factory default state so if your devices are already configured heavily then that may not work and may result in Profile Owner/ Work Profile instead of DO. It's worth a shot however. 

I have started enrolling and managing any of the Zebra Atlas devices as AEDO, even if they're still running M or N in order to prepare for the upgrade to O. I have confirmed that it is a seamless upgrade from N to O if the device is already managed under AEDO on N. I would suggest starting to plan for the inevitability of Zebra Atlas devices and definitely Helios devices shipping or returning from the repair depot with Oreo or higher.

Hey Matt,

So, you're saying there is no way to get from DA to DO without a complete wipe and reinstall?  I've got 1700 TC56s spread over 23 states.  Yippee.

Yeah... The DA->DO migration is no joke which is why Google has been pushing everyone in that direction with each successive version of Android since M.