The reason for 3v being Chord standard DAC OP is more historical. Going back to the 90's, it was common to use passive pre-amps (that is a simple analogue volume control and nothing else), and a common complaint was 2v was not enough to drive power amps with quiet CDs - so I added some more voltage to 3v, and that became the standard OP voltage.
But things have moved on considerably since then, notably with my 100% transparent volume controls and the DACs becoming digital pre-amps rather than fixed voltage out DACs. And I found that the 3v was too high a level for some pre-amps - hence why Qutest had 1v, 2v and 3v fixed OP options. And of course, headphones are needing more voltage to drive them, and IEMs are insanely sensitive, so DAC amps are being pulled in two opposing directions.
So if I had a line level OP it would need to be adjustable, and I didn't want to make Mojo 2 more complicated to control, so the line level feature was dropped.