If you shoot raw, the WB is meaningless. The K values express a range, not an exact color. Every raw processor uses different math and processing to produce the same results. In a nutshell, I don’t see how this would be useful for raw shooters. Film had a very fixed rendering thus using such a meter, and assuming the recipe for compensation filters worked, that was then a useful instrument. Not so much today.
Now if you could get true spectral color info, and then somehow build an on the fly profile (DNG profile ideally for many), such an instrument could be quite useful.