STC Optics, the company that makes the light pollution clip-on filter for DSLR cameras will soon also introduce a new in-body ND filter that will work on the same principle (clip-on filter directly on the sensor). This could be a cheaper solution for photographers who use ND filters frequently - you can use the clip-on filter with all of your lenses (ND filters are expensive).
Another interesting development: NiSi announced their new light pollution cut filter (natural light filter) at the Photography Show in the UK - it looks like a purple/magenta filter, but it is actually a spectrum cut filter for certain wavelengths. The result - it cuts out light pollution from various sources, resulting in a sort of hyper-real cityscape:
