Can you jump from Marshmallow to Oreo directly on a TC75x?

Most likely, yes. But this is strictly speaking, outside of SOTI. Meaning you should be able to upgrade from 6->8 via Zebra provided FPU .ZIP, but that does NOT mean that things will continue to work in your SOTI environment. 

Is it possible to enroll an android 8 with android + ?

NO!

Why it's not possible to enroll android 8 with android + ?

Android+ leverages the Device Administrator API for management and that principal and elevated privilege is going away with each successive version of Android. It is in fact, completely removed from Android 10. SOTI and Zebra together stopped signing the OEM specific DA based agents a little earlier however and therefore support for DA ended with Android 8, instead of 9 or 10. This might still change, but I highly doubt it as both Zebra and SOTI are highly committed to push the Android Enterprise agenda forward. 

Also, could you tell me if there are some big difference between android entreprise and android + ?

YES! There are quite a few differences actually! Android Enterprise has different enrollment strategies, most all requiring the device to start from a Factory Default state. If your Android 6 and Android 7 TC75x are enrolled using Android+ (DA) today then they actually would first need to be Factory Reset and then re-enrolled using Android Enterprise. Those devices will also very likely to be converted to GMS versions of the OS if you are running AOSP today. While it is technically possible to enroll Zebra AOSP under DO it will put the device in a rather unconventional state and you will lose out on capabilities like Managed Play Store distributed Managed Configs and OEMConfig. Did I say Managed Play Store!? That's right, Android Enterprise is going to also likely force more open access to Google's servers so that too could result in changes in your environment. There are many other changes that I have not outlined here but the short answer is yes, there are big differences between DA and DO (or PO!) and you should be well acquainted with them before trying to upgrade your fleet to Android 8.  

All our rules will be work again with android entreprise or we need to review all ?

File Sync Rules should remain the same but other Profiles will need to be recreated as Android Enterprise Profiles as they are treated as a different Profile type. You will likely initially find that there is still not feature parity with Android Enterprise, as Android+ still seems to be more powerful today, but expect that to change eventually overtime. You likely are going to want to upgrade beyond 13.3 as well as SOTI is investing heavily in Android Enterprise features. For example you won't be able to take advantage of OEMConfig unless you are on at least version 14.4.

Here is an aptly timed KB article from Zebra (published today!) confirming that they are no longer signing the agents for Android 8. Therefore it seems to confirm that it is Zebra moving you to Android Enterprise on Oreo and not necessarily SOTI, but then again the OEM signing process did require collaboration.

https://supportcommunity.zebra.com/s/article/SOTI-agent-error-message-This-device-agent-is-incompatible-with-your-device?language=en_US

The writing is on the wall, we all need to have strategies to migrate to Android Enterprise. It is a lot less painful to get ahead of it now on Android Marshmallow and Nougat since you're able to upgrade to Oreo and stay enrolled. If however, you're still on Android+ based management and attempt to upgrade to Oreo, then the devices will need to be factory reset before being re-enrolled under AE.

With all that said, SOTI and Zebra did announce at Sync that they are working on a DA->DO migration that you might be able to perform without a factory reset. I've heard rumors of this for some time but have not seen it in the wild.

Hello matt,

thanks a lots for this long description and also shared your knowledge , now it's better clear for me …

I have a meeting next week where i need to explain the way we will follow for our devices.

I think to end my test of upgrade android 6 to 7 next week.

our way will be this:

a) Migrate all our device to android 7 in first.

b) Install the new mobicontrol admin version -> v14.4 OR 15 actually we are in v13.3.0.34 (3 years installed)

c) Step by step migrate android + to android entreprise

I don't know how to thanks you matt, but it's a real pleasure to spend time here because by your reply with some others guys at some question we learn many.

Many thanks

Hello Matt, I am new to the forum. We are about to upgrade from MC 13.4 to MC 14.4 because my company want to move the MC database from Server 2012 to 2016 like they have already done with other much larger databases. I am running L on TC80s and O on TC83s Androids. Looking at your replies to others are worth Millions to me and I truly appreciate you and others on this forum for providing excellent insight on Soti's and Zebra's mobile technology as I was also unaware that they are about to stop supporting Android+. My TC8300s are profiled as Android for Work in my ver 13.4 environment which I was told was the same as Enterprise. But since all of my TC8000s are Android+: approx:130 and 100 TC8300s I better take a look at the link you provided. Thank you for being here for us all, and like I said, I am new to the forum and I'm sure there are other Matt like individuals here that I will be showing appreciation to also. Thank you.

Thanks!

It's honestly very helpful to understand the overall landscape of Android Enterprise management beyond SOTI so that you can understand what behaviors are specific to one versus the other. 

Jason Bayton's website has been a consistently valuable resource and I highly recommend it to get a better understanding of the world of AE management.

https://bayton.org/2020/01/the-decade-that-redefined-android-in-the-enterprise/