that's what i thought about it being a naomi 2 derivative as well...
i first saw photos of this board 4-5 years ago and since then all we know about it is that it was an early dreamcast set 4.25 devboard paired with a rev. C cross products debug adapter and a gd-rom emulator (not pictured here) made in 1998. Finalized dev hardware is set 5.24. I hypothesized that not all clx2 functions had yet been integrated on a single chip or that sega was experimenting with dual pvr solutions as early as 1997...Anyway, the dating of dc's dev hardware is a bit confusing, they had this board ready in 1997 and the first piece of kit that was massively available to studios was a clx2 pci card with the kamui api on April 1998...
I know a guy who has one, i will try to reach him and get a better picture of the whole setup.