You can use some existing heightfield operators to do this already in fact, although without the tiling (could be tiled in another app though). Here's the quick method - you can experiment further to get better results:
First create your procedural terrain, of course. Now create a Heightfield Generate node and hook up the *last* output of your procedural terrain to its Shader input (on the right). Then specify a coverage size ("size in meters") and number of output pixels in x,z (next to "new heightfield" checkbox). By specifying size in meters you tell it how much area you want it to cover in the world. By specifying number of output pixels you are basically setting the resolution of the resulting heightfield.
Once you're done setting that stuff up click Generate at the bottom. Wait for it to complete (it will take a bit for larger - in pixels - heightfields) and when it's done right-click the node and choose Save File As, specify a location and name and save. Viola! You have an output of your procedural terrain in heightfield form. .ter format can then be converted to just about anything else with freely available tools - TerraConv, Wilbur, World Machine, Blender, etc.
[Edit]o_b beat me to it, but the size specification stuff is good to know.
- Oshyan
