I do love the idea of making old timey printing plates using a 3D printer. If you printed in TPU would that make the equivalent of a rubber stamp?

Probably.

I mean, there’s no reason why a 3D printer couldn’t be rigged up to use a stylus instead of an extruder. (Plotters exist after all.) Probably not very performant compared to your solution though.

Yeah, plotters exist, but they’re slow. The reason I mention subversive literature is that activist groups are some of those that would most benefit from an open source printer option. Regular commercial printers all have government-mandated fingerprinting software built into them. A home made printing press gives you the throughput of an inkjet printer but without the opsec issues.