POSSIBLE & LIKELY
[1] noise improvement: but don’t expect too much: move to a D700
[2] dynamic range improvement: but don’t expect too much: move to a D700
[3] 14MP+ sensor
[4] 1080HP video
[5] 6+fps shooting rate
[6] Drop down/flip around LCD like the D5000 n.b. adds depth to camera; likely if d40 has video capability
[7] improvement in AF
[8] More flexible Mirror-Up functionality
[9] Better, simple implementation of Live View
[10] True centre button on the multi-selector switch (as in the D700)

POSSIBLE
[1] Better Auto WB
[2] Faster face AF in Live View

POSSIBLE & UNLIKELY
[1] In-camera HDR
[2] Auto-Bracketing at 2.0 EV
[3] Bounce-able internal flash?
[4] Weather/Waterproof sealed body
[5] Newest Capture NX included
[6] custom bank should save all of your current settings both shooting menu and custom
[7] Allow any function to be assigned to any button
[8] RAW histograms
[9] smaller body
[10] Weaker anti-alias filter
[11] Live View with exposure simulation
[12] An additional channel in camera for CLS (3 extra groups instead of 2)

POSSIBLE & IMPROBABLE
[1] in-camera GPS – profitable option for Nikon
[2] in-camera Wifi and/or Bluetooth – profitable option for Nikon
[3] Built-in wireless remote capability – Nikon doesn’t seem to see this one because they think they already have it (via the 10-pin). Also, in Nikon’s defense, wireless is a huge design problem. Wireless spectrum is regulated worldwide
[4] more cross points in AF – not likely soon for technical issues
[5] Internal RF based flash control for CLS – Nikon hasn’t fully developed the current iteration yet
[6] Even more customizable buttons – D300 already has too many buttons; too much customization interferes with functionality; maybe some internal bus issues
[7] Small RAW files as an option – Not necessarily a pointless gimmick. Depends upon how they’re created and converted. If you don’t need the pixels, why waste the card space? But Nikon prefers closed propprietary systems rather than giving the downstream user full access to the original data that was captured, without manipulation.
[8] In body VR – way too much work for too little benefit. Nikon already has heat problems at the sensor
[9] Virtual Horizon inside viewfinder – impinges on high-end pro bodies.
[10] 8 fps jpeg shooting – requires a different shutter
[11] Dual CF and SD memory slots – potential issue of mismatching write speeds
[12] built-in IR – requires a user-reachable filter
[13] a less noisier shutter – a long time coming, why start with a D400.
[14] Built-in wireless tethering to a lightweight screen – already available as a 3rd party option; also looks like a profitable option for Nikon
[15] In-viewfinder icon that indicates when hyperfocal distance is achieved: accuracy an issue
[16] A viewfinder shutter like that on the Dx series – impinges on the higher end cameras