Hi, I agree with all requests posted above + I would suggest slope detection with different slope detection thresholds/settings for each object, rgb color rotation/scale variation maps (as the ones in multiscatter) and maybe even some height thresholds too + hand painting/scattering objects while considering those slope detection/threshold settings - well nothing special :)
Slope detection to make such
http://thumbs.dreamstime.com/z/steep-rocky-mountain-slope-landscape-bucegi-mountains-romania-36037323.jpg things a breeze - ugly colors on that photo but it's good as an example :)
Height thresholds + slope detection + variation maps to make something like this
http://3.bp.blogspot.com/-bN0SvgeAn0Y/Uh4jQ97PfyI/AAAAAAAAAtM/Kh60KFH3t-0/s1600/yoho.jpg Well maybe not a breeze but certainly much easier :) Of course one could always use some density/slope maps generated by world-machine/vue/GeoControl or something similar but still density map support is needed for that not to mention other software + some knowledge of its workings. Other method (density maps are still needed) - one could use Gugila's groundwiz's Terrain Map (
http://www.gugila.com/products_gw.php?ID=gw2 ) yet I don't know if it is already supported + that map can be a real ramchewer if baked, well at least in some cases. And another - something like that
http://www.3dm3.com/tutorials/mount/ - still density maps are needed and I suspect you won't get scatterer viewport preview unless that procedural is baked which again can be quite ram consuming depending on the scene scale and details needed.
All those methods can work pretty well, given the support for density maps, still if possible It certainly could be way handier to have that slope detection directly inside corona scatter just to avoid distractions and unnecessary meddling with other soft, not to mention it would make Corona even more awesome :)