Have been looking into the SpaceX Zuma launch and there are a lot of things coming up that are very odd with this mission. First off, the level of testing and care going into this missions is unprecedented. The mission has also been delayed multiple times due to technical concerns with the fairing, engine test data, etc. The launch window is very tight and coincides with the overflight of another SpaceX launched NRO satellite called USA 276. Furthermore, Elon is on record saying this is the "most valuable payload ever launched by SpaceX". At the same time the payload does not seem to be overly heavy as it is going to LEO and there is enough performance left over for recovery which rules out a large recon satellite or any kind of "Rods from God" ridiculousness. So this leaves a couple of options.
1) A new type of small recon. satellite perhaps with hyperspectral capabilities: This is a possibility as Darpa has been working on hyperspectral sensors for many years and the benefits of this technology are many fold. However, the care being taken with it points to the payload being nearly irreplaceable which seems to not match a recon. satellite program where a flight unit and one or two spares would be built as part of the program costs.
2) On-Orbit Satellite Servicing Mission: This is a likely possibility as Darpa has been developing this technology as well for some time and Northrup Grumman has been the partner of record. This theory is also helped along by the launch coinciding with the overflight of NROL-76. But again, if a servicing mission the satellite would be easily replaced and as such does not explain the extreme care being taken.
3) Spaced-Based neutrino Detector for Nuclear Material Location: The gov has been working on a portable neutrino detector for some time to characterize and locate nuclear materials on the ground. Because neutrinos travel long distances and pass through standard matter they are the perfect way to detect nuclear material from afar. The problem is they are very hard to detect and especially triangulate their source. But what if the technology has been made portable, that the prototype is very intricate and expensive, and additional units will not be built until the concept is proven. Furthermore, if it is to be used to detect nuclear material it would be a huge asset to the NK situation. This would explain the level of care being taken with this launch, and the reason why the launch date hasn't move very far each time a delay has arisen. A system like this would make hands-on nuclear verification a thing of the past, and it would give us a HUGE advantage over NK/Iran.
We will have to keep a close eye on the payload after launch to see whether it actually rendezvous with the USA 276 satellite or continues off on it's own path. If it is option 3 then this is the tool that Q and team have been waiting for to gain the upper hand.
Article re. similarities between this Zuma launch and NROL-76/USA-276: http:/ /spaceflight101.com/falcon-9-zuma/zuma/