The blades will remain non-interfering due to the spacing of the axles in which they are mounted. They need to be fixed shafts with bearing mounts. The design should be such that there is a minimum of 3 mm clearance between the tips of the blades. Shims are then used to maintain blade spacing after repeated sharpenings.
Most of them I have seen (including the Stepkovac branded units) use a drive belt (with a tensioner) to drive a gearbox, which is typically attached to a 3rd spur gear that drives the spur gears on the blade axles. This ensures that slipping will occur on the low torque side of the gearbox.
I think the biggest obstacle is working out the exact dimensions of the knife/axle/gearbox assembly and getting it into .dxf files. That would allow anyone to build one by having the steel work done by almost any job-shop anywhere. The plates, bearings, spur gears and gearbox are the big ticket items.
I think everyone here is more than capable of coupling it to a drive system of their choice (pto, gas engine, electric motor, etc) and constructing a feed chute that works for them (I would prefer a horizontal feed personally).
I did find a company that sells just this piece, It’s $1985.97 (converted from Euro to Dollars) + taxes and import fees, which makes it impractical for just about everyone here;
Ideally, I would like to see a pre-fab parts kit with the components to assemble this for a couple hundred dollars. I think that would make it practical for most of the members here. There is no reason it should cost more than this, it could easily be manufactured for under $100, so a $200-300 price tag should make it more than profitable while keeping it affordable. You are probably going to spend about that to build any of the rear axles or bailer based chunkers currently being discussed on the site anyway.
If a gearbox were included, the price would necessarily increase. I have found suitable gearboxes for a couple hundred bucks on eBay (16:1-ish ratio) but again our members can utilize whatever they have access to for driving, the unit. For most of us I think the base cutting system (as shown in the above link) would be sufficient to build upon.
Thanks for the interest!