I agree that 32-bit chips (and decent instruction sets) make everything much easier.

You wouldn't necessarily have to interpret G-code on the 8-bit microcontroller itself, although it's about the same difficulty as interpreting BASIC on it. Keep in mind that keeping the motors of a 3-D printer busy only requires a few speed changes per second, maybe 10 at most. By contrast, the 8051 in an Epson MX-80 printed about 80 characters per second and had to actuate the 9 hammers in the print head with a new set of voltages 9 times per character, for a total of about 700 deadlines per second.

When Don Lancaster was trying to figure out how to build 3-D printers and other "flutterwumpers" in the 01990s, his idea was to use a bigger computer to rasterize curves into a set of one-byte step commands that would be interpreted by an 8-bit microcontroller, for example in https://www.tinaja.com/glib/muse140.pdf, as I mentioned in https://news.ycombinator.com/item?id=42080682. His first explanation of this concept may have been his July 01993 "Hardware Hacker" column in Electronics Now (previously in Radio Electronics and Modern Electronics) https://www.tinaja.com/glib/hack66.pdf where he's exploring the possibilities opened up by Parallax's BASIC Stamp:

> One potential use for the BASIC
Stamp is shown in figure four. I’ve
been doing a lot of work with the
stupendously great PostScript general
purpose computer language. In fact,
this is the only language I use for all
of my electronic design, pc layouts,
stock market analysis, schematics,
Book-on-demand publishing, and just
about everything else.

> All the camera ready figures you
have seen here in Hardware Hacker
for years have been done by using
nothing but my word processor and
PostScript. Device independently.

> The only little problem has been
that PostScript I/O tends to end up a
tad on the skimpy side. Usually you
only have three choices: Dirtying up
otherwise clean sheets of paper or
plastic; writing files to the hard disk;
or returning your data back to a host
for recording or other reuse.

> The BASIC Stamp can instantly let
you extend the genuine Adobe Level
II PostScript to any personal project
or machine of your choosing!

> Assume you’ve got a homebrew
machine that has an x-axis and y-axis
stepper, an up/down mechanism, and
a "both steppers home" sensor. This
can be a vinyl signcutter, engraving,
or embroidery setup. Or an automated
printed circuit drill, a wooden sign
router, or a Santa Claus machine.

["Santa Claus machine" was Theodore Taylor's 01978 term for a 3-D printer; it's what Lancaster consistently called them in his columns over the years.]

> You could use two of your BASIC
Stamp lines for RS423 serial comm
with your PostScript printer. Use two
lines for both x-axis stepper phases.
And two lines for those y-axis stepper
phases. One line for pen or drill or
whatever up/down. And a final line
that zeros only when both steppers
are in their home position.

> The hidden beauty here is that all
of those fancier PostScript fonts and
the level 2 tools immediately become
available for use on your own custom
homebrew rig. At unbelievably low
cost. With zero royalties!

Normally when people do diagonal lines and arcs on computers without FPUs, they don't use floats; they often don't even use integer multiplies per step, but rather strength-reduced algorithms like Bresenham's algorithm and the DDA algorithm Bowyer talks a bit about in https://3dprintingindustry.com/news/interview-dr-adrian-bowy....

I agree with you that additional chips are expensive, but in the overall scheme of things, a few 555s to drive your motors aren't going to make the difference between feasibility and infeasibility.

So I think it's clear that we could have done hobby 3-D printers 40 years ago. What similar opportunities are we missing today?