These old HP "cartridges" were more of hotends with integral extruders. Which means they can be installed onto a printer equivalent of Prusa i3 to turn it into a printer. For a truly open printer, we'd need an open inkjet head - and those are actually made in lithography process, believe it or not.
As long as the cartridges remain available and affordable, I don't see that much of an issue. None of the ICs in the control boards are "open source" either.
Currently, the cartridges are available and affordable - with multiple aftermarket suppliers. Some of which even split the "print head" and the "cartridge" into two separate parts, or leave ports for refilling them.
An open inkjet head would sure be fun to play around with, but it's not a hard requirement.
These old HP "cartridges" were more of hotends with integral extruders. Which means they can be installed onto a printer equivalent of Prusa i3 to turn it into a printer. For a truly open printer, we'd need an open inkjet head - and those are actually made in lithography process, believe it or not.