I've seen this site this is home to a well known application that's called World Construction Set (WCS) which is capable of using GIS and GPS data for a vary different set of applications such as Forestry Management and Civil Engineering and Land Management which require vary different tools and feature requirements then what TG2 is set up to do right now.
If you where going to take Terragen down that route then it would require the ability to make terrain from cartographic contour lines and support things like the import of GIS, GPS and Surveying data such as .Grass and .GEOTIFF as well as satellite, multispectral data and remote sensing data in the optical, x-ray, gamma ray, UV and near and far inferred spectrum and should Handel multichannel-channel complex data sets etc.
I am sure a specialist in the above fields could go on to flesh out the needed features if required in some detail but I am sure one of the major requirements would be a fail safe data structure. All of the above is purely hypothetical but if you where to draw together the respective feature sets of the GIS and related programs together into one application you could have market dominance in these under resourced fields.
Regards to you.
Cyber-Angel