What tools is OS X lacking? From my experience most of the development and server tools are available natively on OS X. It lacks support for containers, but that would be a worthy addition, and I would say worth spending money and time on. The rest is already there for the most part. Developing further their server infrastructure would allow Apple to make a play for the corporate market. Any way, it's a silly argument. I thought they ran most of their backend on OS X, it looks like was wrong.
It's not small server stuff like Apache that they are missing. It's stuff like distributed failover, exotic driver support, SAN, management etc. that they are missing. Big data center stuff, the kind of thing companies like Red Hat make.
Those kinds of products are huge investments. Sure Apple might be able to market towards the enterprise, but they simply don't think there is any money to be made. They used to have for instance Xserve that tried to stay afloat in that market, but which made little money. Since they canceled it, Mac OS has only been developed as a small to medium server (which it isn't half bad at). But big time data centers are a different world.
For instance, as a very basic example, does Mac OS support Infiniband or the more exotic high-speed ethernet network interfaces? For Infiniband, the answer is no and in the other case the answer is "kinda, but not really."
My background:7 Xserves still in production here in K-12 education, 1000+ users in OpenDirectory
In the pipeline:Migrating to the new shiny Mac Pros along with OS X Server
Reasons: Thunderbolt 2 connectivity is amazing and works fine to connect FibreChannel RAIDs.
OS X Server: Though it's correct that the GUI got simplified a bit, it's the same server package and complex as it always has been, however easy enough to support. And if configured correctly, a solid workhorse for many scenarios: network accounts for lab use, calendar and contacts server, along with some helper tools it works in heterogene environments fine, supports huge amounts of users in via LDAP..just to name some reasons. for 20 bucks the best server os to support Mac and iOS clients. And because the underlying foundation is UNIX, it's friendly with any networking stuff such as RADIUS for your WP2-Enterprise wi-fi needs..just to name a view.
One thing that is not quite right in the post above: SAN support exists via XSAN.