Did you factor in the fact that you don't need any clearance on the sides of the pedal?
I have 3 EHX Pedals, now (Hot Tubes, Big Muff, BassBalls) and I love the fact that I can butt them up against each other. You still need clearance at the "top" of the pedal, but I've yet to see a Boss/Digitech/DOD, etc. that didn't require clearance at the top if you run AC.
With the size of the PCB on the inside of the Big Muff, you'd still need a case the size of a MXR 100 phasor. Plus you'd still have to drill and mount the jacks and knobs, mount the PCB internally, and make sure grounding was proper.
The upsides of the larger case is larger knobs. With my BOSS pedals, I have to get low to make sure everything is set right, especially on a dark stage. With the "chicken-head" knobs of my Muff and BassBalls, I can see it and even adjust it with my foot on the fly.
The Muff is also still smaller than most Boutique pedals that I have run accross. And honestly *L* it sounds as good at 1/4-1/6 the cost!!!