I hear ya, totally support your full-suspension efforts here. Correct me if I'm wrong, but I don't think a highly utilitarian cargo bike with an excellent suspension system has been done yet. With what Chalo was saying earlier needing different suspension for wildly different loads - I think adjustable air shocks are the way to go and I like you're suspension link design.
For sure, I don't know if a miniature off-the-shelf air compressor capable of 300+ psi is readily available somewhere, but you might tackle the problem another way. Just design and fit a high pressure air chamber with enough volume for say 5-10 (or whatever) suspension adjustments before it needs a recharge(pump) at home base. Then you just add the necessary hard lines, flow-regulators, flexible lines, gauges, shut-off valves, one-way/check valves, and bleed valves. I'm probably missing some components, but you get the point.
Sounds pretty achievable to me and then you'd be able to make adjustments on the fly if your cargo loads change until the air pressure manifold needs refilling.