The accuracy required for the ink droplets just isn’t there for prosumers.
I can (and have!) built multiple extruders for a variety of 3D printers. Some of my own design.
Sadly, the tolerances for an inkjet are at least an order of magnitude greater.
I have zero doubt that a few clever hardware hackers could design an open source inkjet printer. But A: They’d get sued back to the mesolithic by every printer company with a patent. And B: the process would likely involve micro machining your own hardware.
I’ve just said, “fuck it” to the entire industry. I’m in my early 40s and I’m reasonably sure that my Brother laser will outlive me. And possibly the heat death of the universe.