This feature to cut the ground already exists?
No it was something new, and super cool i think.
It was to minimize memory load if i remember well.
I just wonder, since camera already has a limit, why that cant be used.
I guess its because you never know if a plane is huge, or small,
So a huge surface might disappear to soon once a vertex is out of sight.
Checking all vertexes might cost to much cpu time, and i think they made some kind of rasterizer
So only if a raster is in sight it can have its grass rendered.
That would allow for a a way to render less grass, and having a scene partial into GPU memory.
I wonder if the same effect could be reached with density map, where the map itself had some camera radius overlay (so only render in cam ray)
BTW i liked that gras to i hope its coming to blender too.
Hey!
all of these features I used are nothing new, it can be done in current master without any problems!
I am using a mesh as an input to drive a Vertex Group Proximity Modifier.
http://www.blender.org/manual/modifiers/modify/vertex_weight.html?highlight=vertex%20proximity#vertex-weight-proximity-modifier
(It basically adds the Verticies close to the driving mesh to a vertex group). I am then using this group as an input to a Mask modifier (this hides the vertices that are not in the group).
http://www.blender.org/manual/modifiers/generate/mask.html?highlight=mask%20modifier
The driving mesh in return is deformed by an armature which basically lets us access these options from a linked group outside the file.
The particles are emitted afterwards in the stack, which of course gives some issues with particle density dramatically different patch sizes.
Also the grass stuff is possible with current blender, no code wizardry here. My plan is to publish a series of tutorials about all this stuff on the Blender Cloud after the production. 
Cheers!
.andy