It has been done - '20s UK.

It was a commercial failure. Partly because it was launched at a time
when complex mouldings were going out of fashion, partly because it
used the new diecast-zinc alloys. At the time (before Zamak / Mazak)
these only had a service life of a few years before warping out of
shape.

It was slightly different from your idea. The sole was made from
stacked units on pins, but the irons were one-piece.

One other benefit / drawback of this design was in "springing" the
plane. Most complex moulders aren't used square-on to the timber,
they're tilted over or "sprung". The ideal spring angle is a factor of
the overall moulding, not the components, and so a component-based
plane would be at a disadvantage because it would be built around a
single standardised spring angle.

There is however the possibility of such a plane, with separate irons,
being made to have ideal spring for each section of moulding. If you
could make it workable with so many narrow closed mouths, then this
might be a useful advantage.


It's also not unknown to see a #55 (or usually one of the simpler
models like a #50 or a Record #43) that has been custom-fitted with a
closed mouth block and used to make a particular moulding for all of
its life. I've got a pair of these from a coffin-maker, the case
moulding and the lid moulding.


Incidentally, " the negative-image contour of the moulding" is known as
the "mother plane". These were valuable individually-made planes, made
either by hand-carving the first example of the moulding (the first
mother) with scratch stocks and chisels, or later replaced by one
worked by its own offspring. There are tales of 18th century plane
makers saving them from fires, listing them separately in wills etc.
Owning this set of mother planes was pretty much the definition of
being in the plane-making business.