Why wouldn't it? The DNA 20 can deliver 6 amps. With a 0.7 ohm load, you're not pushing the current limit until 4.2V; the trouble is you're hitting the power limit of 20 watts at around 3.75V.. The biggest problem I see with such a low resistance load is that it you're only going to be able to operate it in a relatively narrow range of power, roughly between 15 and 20 watts.
What puzzles me is why one would want to run such a low-resistance coil on a DNA 20. A low resistance coil is needed on a mech mod, 'cause that's the only way you're going to get serious power out of it. But on a DNA 20 a coil in the range of 2.0 - 3.0 ohms will still get you the full range of power (7 - 20 watts) and seems much more sensible, no?
The DNA20 will send the full power of the battery through if you set the wattage lower then it can step down the voltage to, so it is possible to get over 20 watts, and it is still "protected" by the DNA20 to some degree.
Your absolutely right that going that low in ohms is not needed for the DNA20 devices, and kind of restricts some of what you can do.
I wasn't really targeting .7 ohms in that build, I was actually gonna just do a single coil build, but happened to have just enough left over kanthal on the piece I cut to do a second coil, and figured what the hell.
I am still having a lot of fun playing with all the variables in coils, inside diameter, kanthal guage, total length, style of wrapping, methods of wicking, ect... It is really nice to be able to push anything from a 0.7 ohm coil, all the way up to like a 4 ohm or more if you wanted to, all on ONE device.
So yea, sub ohm isn't needed on DNA20 devices, but it is doable, and really just becomes another option in your tool belt when it comes to playing with coil design!