COLLADA should have the possibility to specify normal maps, height maps, and displacement maps - in every standard COLLADA shader/effect. With an additional factor for the scaling.
While modern programs support much more factors for normals maps, height maps, etc., at least the common basic forms of this texture maps would be supported.

For example, normal maps are a so common feature, that even primitive gaming engines offer that today as a minimum.
And it's everything else than a stranger in 3D modeling software.

The need for that feature can be seen, for example, in the Feeling Software COLLADA exporter, which implements the <bump> tag for normal maps.