i hope i can say that hyperion will push for a full W3D release with the shipped version of OS4. if they dont it will be a big mistake.
Of course the final OS 4 will contain Warp3D, in fact the next update will probably come with full hardware acceleration for Voodoo 3/4/5 and ATI Radeon's. However, with the drivers still in beta, it doesn't make sense to release a version with hardware rendering.
About the speed, most of Freespace (unless cap ships are visible) is exactly that - free space. No hardware accelerator of anything near Voodoo class will even remotely get into trouble with that. The point really is, as KennyR said, better looks - filtered textures to remove bockiness, alpha blending for engine glows, better particle effects, true-color graphics (the software renderer is 8 bits), these kind of things.
