You can already partially do this with the stock M700
Press Q to steady your aim briefly (up to 5 sec. by default).
In gunspec the settings are in the ;// Accuracy section
simplezoom = 10 (zoom magnification intensity)
accuracy = 100 (hipfire accuracy - poor)
runacc = 300 (running hipfire accuracy - awful)
simplezoomacc = 0 (zoom accuracy - pinpoint)
zoomaccuracy = 30 (zoomed breathing sway intensity)
zoomaccuracybreath = 5000 (maximum time in ms that aim can be steadied before needing to reapply)
zoomaccuracybreathhold = 1 (0/1 toggles this feature off/on for this weapon)
zoomaccuracyheld = 1 (zoomed breathing sway intensity when steadied)
zoomholdbreath = 16 (keybind. This line can be omitted in gunspec as it is now defined globally in setup.ini)
There is currently no crouch aim accuracy modifier. I agree that it could be good to have but Lee would need to add several variable settings for it. There has been talk of proning in the past but I don't see it happening any time soon. There a ton of animation and function related dependencies that would need to go along with that and there are more pressing issues for them to deal with.
Gigabyte P67A-UD4-B3, Intel Core i7 2600K (passmark 8555), 16GB Corsair DDR3, EVGA GTX 970 SC (passmark 8637), Win7 Pro 64-bit SP1, Primary monitor @ 1920x1080, secondary monitor @ 1024x1280