Konami

GX Type 1

• Racing Force
• Konami's Open Golf Championship

Both of these games use a special ROZ layer generated by the "PSAC4" custom IC which appears to include a height map.

GX Type 2

• Fantastic Journey

This game (the export version of Gokujou Parodius) uses a protection chip to write to the palette.

GX Type 3

• Soccer Superstars

This game would probably work if the video emulation were simply sorted out a bit more.

GX Type 4

• Run and Gun 2
• Rushing Heroes
• Versus Net Soccer

Each of these games has a Xilinx FPGA (different per game) which primarily acts as a DMA controller, copying things all around work RAM and into the palette and sprite RAM. However, the format of it's operation list is not understood (see the comments in src/mame/drivers/konamigx.c for more details).

Polygonet Commanders

The 56056 math DSP is not fully emulated, and neither is the network hardware so the game's getting cranky at the moment.

GV System

All games on this system suffer from a corner case involving audio track playback in the SCSI CD-ROM emulation.

Bemani Twinkle

• Beatmania IIDX series (prior to 10th Mix)

This PSX-based hardware would certainly be possible (probably even easy) to emulate, and Guru has many of the CD-ROMs in hand.