No evidence
as yet for extra DR.. you're probably correct in assuming that downsampling from 14-bit (raw) to 8-bit (jpg) will simply result in more accurate rendition of colour graduations - a decent enough feature in of itself
The other way to look at it is with high-DR scenes; adding more bits per pixel
should allow for better recovery of blown highlight data when shooting in RAW, since there is greater mathematical precision involved in the storage - and thus recovery - of highlight tones.
Of course this is all conjecture at present and won't be proven until the first production models start finding their way into the real world and the hands of working photographers.