2) What are potential solutions?
- Support Centroid Sampling
- Use Pixel Shaders to Clamp Texture Coordinates
Centroid sampling doesn't have the problem that center sampling does in multi-sample antil-aliasing. ATI has supported this form of anti-aliasing for the 9000 series. The tricky part is enabling this when DirectX doesn't easily expose this.
There's a different trick you can use with hardware, such as NVIDIA's, that doesn't support centroid sampling. Basically you trade off some pixel shader bandwidth to clamp the texture coordinates so that you don't sample texels outside of that polygon's lightmap sub-rect.
Between these two approaches, multi-sample anti-aliasing artifacts should be a non-issue for any DX9-level hardware running Pixel Shader 2.0.
3) How will this look?
We'll release one of the demo movies with the anti-aliasing artifacts in and one with the anti-aliasing changes.
Carmack has probably gotten more than any of you can even dream of