I have considered that layout, which would suit any piano player. But for this first one, I’ll make the left hand a mirror of the right hand. So just like the right hand side, the low notes will be nearer to the mouthpiece. Like this photo:
This is for 2 reasons:
1) The air source will naturally reach the low notes first. If the low notes were at the bottom, the air would have to be diverted to reach the larger reeds first. In other words, its natural for the instrument to be set up this way
2) Although it will take some initial practice, I think this system is ultimately much easier for the player, as the left and right hand make the same movements to play the same notes. Anything you learn with the right hand can be played with the left in the same way.
With a piano, the brain has to deal with 2 systems at the same time. This confuses me, and I hope this unified system will be more intuitive. It also reflects and builds on the trend of 2 handed melodica players, where the left hand reaches over from behind the keys.
I may make the left hand one octave lower too!