Does anybody use one of BM new video assist offerings? They claim that it records 10 bit recording in 4:2:2 ProRes and DNxHD footage on DSLRs via HDMI. I wonder how thats possible when for instance a Sony A7s/r 2 only records in 8 bit. My impression is that its just up-sampled.
Would that add any benefits to editing and grading?
The recorder certainly does record UP TO 10 bit 422 containers of video.
You still need to feed it 10 bit 422 though if you want to fill that container. Otherwise if you feed it 8 bit it will record those 8 bits into a 10 bit file. You'll have a marginal advantage, but it's not turning 8bits into 10 bits.
You can also choose other flavours of quicktime to record to as well, and there are also 8 bit versions of ProRes.
You will find though that the compression of ProRes 10 Bit 422 is likely still better than the internal codec would be.