The timing is certainly right. Nikon's D5000-series cameras seem to be following a one-year cycle, and the D5300 has now been out for a little over a year – it's at the top of Techradar's 'watch list' for new cameras. If Nikon does announce the D5500 at CES in January, as reported by Nikon Rumors, it's pretty much when we'd expect it.
But how do you improve on a model that already does practically everything? The existing D5300 DSLR was launched late in 2013, and has a 24-megapixel APS-C sensor with no anti-aliasing filter for maximum detail, built-in Wi-Fi for smartphone remote control and image transfer, and built-in GPS.
The D5300's sensor is still pretty much at the cutting edge – only the 28-megapixel BSI sensor in the new Samsung NX1 offers more megapixels – so it seems unlikely there will be any headline news here, although Nikon does routinely announce sensor design improvements and improved picture quality with new cameras, even if the sensor appears the same.
The rear screen on the D5300 is articulated already, but the tip from Nikon Rumors is that Nikon will add touch control, which would seem a logical step, especially for video. This would be a first for Nikon DSLR, but a long overdue move if it wants to keep pace with rival Canon cameras – the EOS 100D, 700D and 70D all have touch-screen displays.
It would be good to see a full swap to Nikon's new collapsible 18-55mm kit lens, first introduced with the D3300. It's a lot shorter than Nikon's regular 18-55mm optic and a much better match for this size of camera. The existing D5300 is currently being sold with either the old or the new lens, depending on the retailer and the territory.
It would also be good if the D5500 could address another weakness – the sluggish performance of the contrast AF used in live view mode. Again, Canon is leading the way with this in its DSLRs. The EOS 100D and 700D use the company's Hybrid CMOS AF II system for faster sensor-based autofocus, while the 70D ushered in Canon's revolutionary dual-pixel AF system.
The D5300 was the first Nikon DSLR to have Wi-Fi built in, and Nikon has had a little while now to develop its Wi-Fi transfer and control system. More control over the camera settings from a smart device would be the most useful improvement here.
The inbuilt Effects mode is in need of an upgrade too. This is a key area for the D5000-series cameras because they're aimed at photographers who want to start experimenting. The current effects are fairly limited in their scope but, more importantly, it's not possible to shoot a raw file at the same time. It's too much of a leap of faith to ask photographers to commit to an effect they can't change later.
Nikon does need to be mindful of the new camera's position in the range. The D5500 would need to improve significantly over the older model without cannibalising sales from the next one up in the range, the enthusiast-orientated D7100.
Given the strength of the existing D5300, that might be easier said than done, though they are very different cameras. The D5300 is aimed at advanced beginners, with a novice-friendly interactive display and simplified controls, whereas the D7100's larger body, twin-dial controls and more advanced features are aimed at more experienced photographers.
Having said that, there are rumors of a replacement for the D7100, too. This is another camera on our 'watch list', so you can expect to hear more about a new D7200 before very long.