This is a very Hacker News usage of the word "just".

It is, but I mean: Many of us do just exactly that with 3D printers.

We get a new 3D-printing machine and install our own build of Marlin on it, or move it all over to Klipper. Sometimes that involves replacing the entirety of the brain-box controls and that's just par for the course.

At its root, it's only some stepper motors, fans (more motors), sensors, and heaters that are used in very particular ways.

That's pretty similar to a Cricut machine, isn't it?

Only if done over a weekend

The modern equivalent is "Just" use Fable or Sol to reverse-engineer the protocol, then write new control software that works locally the way you want to work, using the file formats you want to use.

There is no longer any reason to put up with hardware like Cricut that doesn't do what you want, or that includes artificial dependencies on remote servers. If worst comes to worst, then yes, have the clanker write a new controller.