I like the idea, it reminds me of Battlefield Vietnam and some of the sniper escapades me and Reed used to get up to.
However, I don't think it would work too well in DP, sadly.
There are problems with making the textures Mist, as when you are positioned inside the mist brush crouching (as you said the grass would be taller than crouching height), you'd just see the inside of the texture and be invisble to someone looking at the grass, which wouldn't be very good for gameplay or visually. So if you were to make a transparent grass texture, you'd have to replicate the brush many times right next to each other, so it wouldnt just look like the grass had grown in geometric shapes (the faces of the brush), which would be suicidal r_speeds wise. As for using models, not only would someone have to make the models, to be even vaguely realistic they'd probably be very high poly count models - if used in the numbers i'd expect you'd need to make it work, the epolys for any given scene would be spectacularly high.
So as for the long grass idea, its probably unimplementable in DP, or at least very difficult to. Plus, sniping and such isn't too popular in the DP community at the moment, the emphasis is on speed and fun jumps, etc... which personally I think is a shame.
Thinking about it, maybe something like a cornfield type map might be a little more doable, with careful consideration to a custom model for the cornplants (to be used effectively but sparingly) and clever texturing and tunneling to give the illusion of a deep cornfield with silos and windmills, etc... for your sniper towers. Plus you could stick in some agricultural machinery to satisfy your lawnmower needs
.
Just what struck me anyway,
- Dagless