This plan raises some significant questions: Is OS X "datacenter grade"? Would creating such a product offering send the wrong message about OS X? Am I suggesting that enterprises could or should standardize servers on OS X? The answer to that last question is no, I don't think it's made for that. - Fraser Hess
Fraser Hess argues the future of OS X Server lies in virtualization now that Apple has moved away from dedicated server hardware.
I argue that if you want to know the future of OS X server you need to look no further than Caching and Profile Manager.
These are the two features Apple is improving year over year and, in case of Caching, only has a use on premise, not in a data center.
Caching has a clear benefit for users and it's the service that requires zero knowledge of servers. Install server.app on any device that's on 24/7, enable the caching toggle and done. You need no server hardware for this, or any specific network configurations. You only need a Mac that's online and turned on during office hours to benefit from this feature.
The other side of the coin is Profile Manager. Apple needs this service to provide easy deployment of third party services on their hardware. It can be installed locally on a Mac and it does require some decent knowledge of your system and services. It's specifically build to integrate OS X and iOS with existing systems. It doesn't require powerful hardware, but it requires a lot of knowledge and experience. Apple will push Profile Manager as an add-on to their client hardware and as an easy way to integrate those devices in your existing network.
But services like email, calendaring, file sharing, directory services? Others do this better and bigger. The future of OS X Server doesn't revolve around these, historically, core features of a server. The times where Apple provided these office features is gone. Microsoft's Exchange platform does better and runs on dedicated hardware in data centers. No, I don't believe Apple is going for that market. They left that when they deprecated the Xserve. The only reason the software still offers these services is to serve the lightweight user, very small companies with a small on site server that require a bit of this and that, but nothing too heavy.
I truly believe that Apple sees OS X Server as a lightweight on site platform that's installed on top of OS X in order to facilitate using OS X and iOS in enterprise.
It lowers bandwidth by caching updates with zero configuration on these clients, and it automates service configuration on those devices with Profile Manager to take away user frustration. Because it just works.