Thought about it as well but the analog section/input panel is the problem on size. You need access to the pre's gain knobs.
Back panel: XLR, TRS, ethernet, power jack
Front panel: power/phantom switches and LEDs, gains, headphone, iOS jack
That should fit, no?
I would also like to add to the front panel some RCA outs jumped off LR outs, and if I had enough space, some A/B switches to add two more pairs of inputs to toggle with 13/14 and 15/16.
And, if the circuitry isn't different between 1-12 and 13-16, put combo jacks on all inputs.
Maybe even use XLR outs (or have XLR and TRS) for the Aux.
Again, it's a project, might as well see how much can be done. The above enhancements are all basic electrical connections.