the only way we're ever going to get reasonable performance on Android
Maybe, maybe not. If you want to truly replicate software, there's still a lot of work that's going to have to occur on the CPU. In a perfect implementation, you would be able to disable the Z-buffer and accurately draw the entire scene -- this means clipping polygons in screen-space and other wonderfully enjoyable tasks. It's going to be the only way to replicate a lot of effects, including proper ordering of translucent walls/floors.