OK, so there is not precisely "nothing" new in AD 2019, but as a management summary it will do.
Before you read on I would like to make it perfectly clear that:
- This information is not official in any way.
- All information here is based on public information.
I had a look in our documentation for new functionality in Active Directory and I found ... nothing. So I dug around a bit and started with the updates to the schema because new Active Directory features generally require a schema update. And yes, there is indeed an update. There is just one new file called sch87.ldf which adds just one new attribute called msDS-preferredDataLocation and raises the schema version to 88.
The new attribute is associated with users, groups and contacts. It is documented on MSDN which indeed says that it's a post-2016 update. What does it do? My best guess is that it is related to Azure Active Directory which also has this attribute. That's all I could find for now. Update 12/2/2018: see the comments for some useful discussion.
Another good question would be: are there new forest or domain functional levels? And the answer is, for the first time: no. The highest functional level offered by dcpromo and other GUI tooling is "Windows Server 2016".
That's interesting. In all earlier versions of Active Directory you could use the Domain Functional to make sure you could not install DCs with earlier operating systems. Because there is no functional level for Windows Server 2019 you cannot enforce using Windows Server 2019 DCs only. At best you could enforce a mix of 2016 and 2019.
Other than that I am aware of some bug fixes and internal optimizations, but that's about it. I guess that the good news is that Active Directory backwards compatibility with Windows Server 2016 will be very good. Any application or device that works with Windows Server 2016 should have no problem with Windows Server 2019.
As usual, "working" and "supported" are very different concepts, so keep that in mind. In particular Exchange and Lync (sorry, Skype for Business) are famous for being very strict with supporting new Active Directory versions.
So, summarizing, what new stuff do we have for Active Directory 2019 compared to Active Directory 2016?
- one new attribute with an as-yet unknown function.
- no new functional levels, which is a first.
- Backwards compatibility should be better than ever.
Almost nothing 😃
Update 12/2/2018: one of the "internal optimizations" that I was aware of is an improvement in handling the Version Store, which is a memory buffer needed to handle database transactions. If you run out of space here, bad things happen such as the DC stopping to respond. My colleague Ryan Ries has now written a really (really) extensive blog on this improvement: Deep Dive: Active Directory ESE Version Store Changes in Server 2019. Considering that he wrote the code himself he deserves a little indulgence here.