The manufacturers make so many models and change them so often that a project to make firmware for them really is not feasible since which printers would it pick?
That said, there are some people modifying the proprietary firmware to disable DRM. They have only done a small number of all of the printers have have such chips in them:
I'm not a printer guy, so this may be a dumb question. All those many models with all their differences and changes - to they not all accept a simple postscript file?
Many decades ago when I was a unix admin, you used to just dump a postscript file to the printer device, and it would print. From a quick google search, every printer I see has postscript drivers - from hp to epson to brother. PS is open, you don't need a driver from the vendor to make a PS file - you can make it with any software you want.
So if this is true (and maybe it's not), then the reason there are no open source printer drivers is because there are, and they've been around always, and the same one will work for all printers, because PS is a standard that's not printer-dependent.
Unfortunately, accepting a ps file is _very_ premium feature nowadays. Nearly nothing in the consumer space does it. I'm still using an old Samsung monochrome from the mid-00's (which, if my memory serves, cost about $50 back then) and to replace it would be four figures _just_ to match the postscript functionality last time I looked around. (And god forbid you want something that understands PCL.)
The topic is open source firmware though. There's plenty of open source drivers and many of them are based on the printers accepting standardized formats.
Hold on, the topic of the comment to which I am replying, is printing with 3rd party ink.
Many, if not most printers do not block 3rd party ink with firmware - it's the driver in windows that blocks that stuff. Many, if not most, block it with a driver in the OS.
The link in the comment above is a collection of firmwares.
Drivers can in essence have hotlists for additional filtering or be given access to communication with an ink chip by the firmware, but AFAIK downgrading a driver doesn't work because what has really happened is it updated the firmware.
A driver upgrade can also never be sufficient for blocking copying on a MFP printer, a standardized net print protocol as you mentioned or using open source drivers either on Linux or under WSL.
That said, there are some people modifying the proprietary firmware to disable DRM. They have only done a small number of all of the printers have have such chips in them:
https://inkchip.net/model/