I'm a big fan of using subdivision on terrain in games for increasing their resolution and adding a certain feel to the terrain. Although it's more space-efficient to do it on load, for small terrains it'd be much easier for me if World Machine supported subdivision upon export. Please consider adding it!
Nice idea but.. wouldn't it make more sense to render the terrain in a higher resolution in the first place?
Yes, please consider adding the ability to export as a Pixar SubD surface, or some other form of loss-less 3D format such as NURBS. SubD is much better than a higher res version of the terrain, and requires potentially less from your GPU & CPU. If not these, then at least incorporate a smarter mesh optimizer, which reduces the polycount where there is little detail, and increases the polycount where there is need.
As it stands now, the Mesh Exporter has a lot of room for improvement. It doesn't optimize the mesh topology in any way before exporting. The current exporter uses a uniform distribution of quads & tris, regardless of topology or detail. A smart exporter would incorporate some form of optimization. The current optimization is too simplistic.
I can't say anything about subD support, but I can say that the mesh optimizer will get much better sooner than anything else. Specifically, a new simplification mode that attempts to optimize for "quality" relative to the kTri target you specify, including a quality mask you can supply to show areas that need to retain higher detail.