Well, I wonder how ISO 51k RAW will look like in APS-C. Or even at 102k. If sometimes my 5D3 gets to its limits @ 25k and 51k. Might a thouroughly new sensor tech make that possible...? With these specs a next update of a 5D could see native ISOs 100-51200 (L 50, H1 102400, 204800) and an 1Dx (H1 204800, H2 409600) !!!
But, let's keep in mind what NL also added:
"Not from a well known source, so I'm still looking for confirmation of different aspects."
Get a 7d file and push it to 25K iso. Thats the best case 56k scenario.