macOS Server has - for the past few years - increasingly become the least-favored child in the Apple lineup. In the last half-dozen or so releases Mac admins have seen the finer points of granular control over services and users stripped away. We gnashed our teeth when they took Server Admin and Workgroup Manager from our cold, dead hands, and screamed defiantly at the angry, stormy night when other services became deprecated or disappeared completely (I'm looking at you, FTP and WebDAV).
And now, to add insult to injury, Apple blithely announced that they're removing the following from Server.app: Calendar, Contacts, DHCP, DNS, Mail, Messages, NetInstall, VPN, Websites and Wiki. And I couldn't be happier.
Let's face it; OS X Server has - for the great bulk of users and admins (and for a long time) - been kind of a relic. Sure, if you jump in your Time Machine (and incidentally, the Time Machine service has also been dumped in its most meaningful sense) back a decade or so then it seemed like a very good idea to be hosting your own email, websites and collaborative services on your own server. External web hosting was a thing, but if you polled businesses and organizations then a decent chunk of them hosted their own email rather than negotiate with (usually dreadful and restrictive) email hosts, and hosted their own contacts and calendars simply because there was no other option.
Network-centric services (DNS, DHCP, VPN) were handy to have too; the appeal of having your own dedicated toolbox was compelling once you considered that you were hosting your own mail, web, and contacts - if only because OS X Server made those things easy and quick to configure. In a world where you often had to make a phone call and sit on hold for twenty minutes in order to dictate a DNS entry to the nice lady at your ISP, this was a critical advantage. (Side note: the nice lady I'm thinking of was Kristin at SeaNet. I had to call her so often that we ended up trading Christmas cards for a couple of years.)
But it's the nature of things that they change, and almost everything on that list of disappearing services is hopelessly underpowered and outdated, and easily available in a better form in the cloud. Mail/Contacts/Calendar? Hello, Gsuite. DHCP/DNS/VPN? Lots of inexpensive and good quality routers and appliances out there. Messages? Slack, or Discord. Some people will mourn the passage of Wikis, but let's face it - Wiki Server was never exactly what you'd call full-featured or easily/fully customizable, and there are third party options if you really need to go that route.
So, what does that leave? Pretty much just Profile managements, file sharing and Open Directory. Apple has doubled down hard on iOS and profile management, and it's a move that is either puzzling or has yet to pay off. Sure, the Device Enrollment Program is super neat (after all there's nothing quite like having your devices set up automatically the moment you take them out of the box), but for ongoing management third party solutions like Jamf do a better job and offer cross platform options to boot. File Sharing has been rolled into the client OS, and I get that - it's a fairly simple thing to set up and being able to set up your Mac to share files dates all the way back to the System 6/7 days - but there's still value in being able to do granular configuration from the command line or the Server.app.
All in all then? There's a lot of smoke but very little fire in this new position. Open Directory is still an incredibly flexible and powerful way of handling authentication and services on a Mac network and there are excellent third party solutions that you can bolt into macOS server that are as good (or in many cases better) than the aging built in ones. There's already a certain amount of vitriol being bandied about the Mac admin community about this upcoming change, but IT admin is a constantly changing pursuit; sometimes you have to throw away your old tools if they don't work and just learn to use new ones that do.