This shake up in nomenclature is likely to keep Dxxx names reserved for full-frame cameras like the D610 and D800. Meanwhile, the extra 300 in the name might just to keep things from getting too confusing between the Nikon D3300 and D5300 that are already part of the companies DX line.
Naming theories aside, this is another bit of news that adds credence to the theory we will see a new Nikon D300s replacement this year. After nearly four years, Nikon D300s fan might finally get the new pro-level DX DSLR they’ve been waiting for.
Via Nikon Rumors