That’s safest for sure. Many printers can connect to the local network so that anyone on the same network can print to them. Some broadcast that service locally so that computers (with the correct software support) automatically detect them, though some don’t. Either way, the actual printing is done by sending data to a local port on the printer (targeted by IP address).
UPnP is a protocol that (in this context) lets devices on a local network request the router to forward Internet traffic on a certain port to a local device’s port. So rather than just local network devices being able to send print jobs, anyone on the internet could. It’s commonly used for web services or multiplayer video games.
Plus the MC shader community’s “LabPBR” texture format is awesome. If Vibrant Visuals on Java uses the format they did for Bedrock, it won’t support some really cool texture information. Plus shaderpacks often include effects far outside the scope of VV, so I think there’ll remain reason for something like Iris to exist. I’m excited to see the possibilities for hardware accelerated raytracing on Java with this change, though!