pianoloverus AFAIK the soundboard in these digital piano is excited by transducers - basically a special type of speaker thatโs attached directly to the soundboard and, instead of moving air themselves, transmits vibration to the soundboard. Kawai gave this explanation on their website.
This mechanism, in theory, can be used with all digital pianos, not just hybrids. I suppose it is the additional cost that make transducer and soundboard not available in low end DPs. Also the soundboard in DP is usually significantly smaller than their acoustic counter part. I read that some DP only use the soundboard for mid to low registers, whereas treble is still produced by traditional speakers.
Here is back side of a Kawai showing the soundboard:

Now, the proposed NV12 video did not mention adding any soundboard. Nor does NV10S appears to have much space to allow a soundboard of good size.