Would you please elaborate on the description of the machine you're looking for? It seems to me that a router with a straight bit with a bearing (such as
this one, or maybe one with the bearing near the collet), and a couple of clamps to hold your stock and template together, would fit the description of a "human powered copier router".
If you're thinking of a pantograph-like machine, but relying on linear bearings to keep a rigid assembly of router and "feeler" parallel to one axis, MakerSlide and other linear bearing systems are useful only with a very large wheelbase, or with bearings very far apart. Otherwise, they'd rack when driven manually. This could be fixed with cable or belt and pulleys -- look up "drafting board" for an idea of how it used to be done, before they switched to a pantograph system (and then to CAD) -- but I have the feeling that it would not be easy to make it precise and sturdy enough.
Why wouldn't a CNC machine fit the bill? Mechanically, it may be easier to build than something that has to handle manual movement. Granted, there's the expense of the stepper motors and the electronics to drive them. It totally depends on your stance: if you're looking to get a job done (and it's a job that could conceivably be done with a Dremel and a very, very steady hand and lots of patience), a machine like the ShapeOko or eShapeOko is a proven concept, can be scaled to a reasonable size, and the extra expense of the motors and electronics is justified (and may even be offset by the simpler mechanics). If you're looking to build something for the sake of building something new, then by all means, experiment, play, improve, have fun!