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The open-source, DRM-free Open Printer shows off a working prototype
(www.techspot.com)
This is a most excellent place for technology news and articles.
I would be surprised if a cartridge being discontinued would kill an open source project like this. They could switch to a different cartridge.
I'd assume they're doing the one for now because it's cheap-ish and has widespread availability. There's little reason not to expand to other cartridges once the rest of the printer is more stable.