MS9288C eval board, aka really cheap VGA to HDMI converter box has arrived and works as advertised. Pinout appears to be similar, though not identical to the MS9288A, for which I found several sources.
What's strange is that none of the VGA pins needed for EDID or legacy ID are connected, yet two laptops detected it as monitor.
But how? Are the 75 Ohm RGB termination resistors sufficient for detection?