It would be nice to be able to use the primary texcoord array for the lightmap, so that you can merge a lightmap and model texture into a single texture, like many of the staticmeshes in UT2004 do. Designing a user interface for this might be a little tricky, so if it could just save out the lightmap that used the original model texcoords, I wouldn't mind merging the lightmap and texture in photoshop.
It would also be nice to have a new lighting mode specially designed for creating shadow details on meshes. The rules would work like this: If a light illuminates a lightmap texel, that texel is full-bright, and is not modulated by the light angle and face normal. If no light affects a lightmap texel, due to the orientation of the face normal, that texel is full-bright. If a light affects a texel, but is occluded from hitting it, a uniform shadow color is drawn.
This way you could create a single directional light, get some baked-in shadow detail, and use vertex lighting for the "real" light effects. When you do these baked-in shadow details, you only want the shadow detail, you don't want any strong sense of where the light is coming from.
It would also be nice to have a new lighting mode specially designed for creating shadow details on meshes. The rules would work like this: If a light illuminates a lightmap texel, that texel is full-bright, and is not modulated by the light angle and face normal. If no light affects a lightmap texel, due to the orientation of the face normal, that texel is full-bright. If a light affects a texel, but is occluded from hitting it, a uniform shadow color is drawn.
This way you could create a single directional light, get some baked-in shadow detail, and use vertex lighting for the "real" light effects. When you do these baked-in shadow details, you only want the shadow detail, you don't want any strong sense of where the light is coming from.