found an unanswered question about Model 4 posed to Real3D
http://www.hardcoregaming.com/spotlight/r3dint.htm
in the mid to first part of the late 1990s, companies like 3Dfx, Nvidia, ATI, could not provide SEGA with an absolutely technically superior successor to Model 3. not even PowerVR could (not until NAOMI 2).
by the time the NV20, NV25, R200, R300 came along though, Nvidia or ATI could have.
but, the arcade market has died up for the most part. there is no longer a 3D arms race between Sega and Namco. console technology is leading the way.