The Magic Lantern team has given the Canon EOS 5DMark III approximately 1/2 additional stops of dynamic range which show numbers of up to 15 stops of DR when using this feature combined with the ‘dual_iso’ module that Magic Lantern already includes in their nightly builds.”
Magic Lantern has been successful in enabling dual/ISO video, but with alternating frames and some motion limitations. Canon 5D Mark III will soon get a “sensor update”. This new feature will soon show up as nightly build from ML.
Magic Lantern Improves Canon 5D Mark III Dynamic Range up to 15 stops
From CR forum user Marsu42 :
This means that for example on 5d3, iso 800 with ML has more dynamic range than iso 100 with Canon :-> … and at high iso you’re getting 7% more dr which is nothing to sneeze at, esp. since it builds upon Canon’s advantage vs. Nikon: d800@6400 = ~8.3 & 5d3@6400 = ~9.4 ev making good ol’ Canon the superior sensor for low light high contrast shooting, esp. the newer 6d.
Since this is a new software at an early development stage, use the necessary attention and do not try it if you are not sure what you are doing.