Tone Matrix Part 1: Overview

For the longest time, I've wanted to build a physical tone matrix. If you've never seen one, they are pretty fun grid-based music synthesizers - here's one in software. I've kept bouncing back and forth on what features I'd want, but I think now is a good point to start locking it in and actually designing it. Here are my specs:

1. Modular: I want to be able to expand it in x (number of steps) and y (number of tones) as much as possible. The final mixing and selection steps will probably require some quantization (increments of 4 or 8, for example) but that's fine with me.
2. Analog: I'm a mixed-signal designer so I want to flex my analog PCB skills for this.
3. Options: Switches, LEDs, wave-shaping, echo, filters, etc, you name it.

I drew up a quick block diagram of what I want below:

The left-most column will be all the oscillators. Each will be tuned to a set frequency (probably pentatonic for ability to always sound nice). The center grid will be the switch matrix design. Each cell will have two inputs, two outputs. Left hand side will get the input from the original oscillator, which will just pass right on through to the right hand side. The top side will input the sum of all previous switches, and the bottom side will output the incoming plus the added oscillator tone from the left hand side. At the bottom of each column is some tempo control and selection logic, which is finally passed to the amplifier/sound effects blocks. I might add a speaker, or just a headphone jack, depending on what total power ends up looking like.