I have a working NeXT workstation with a monochrome monitor and working system keyboard and mouse. Running the original NeXTSTEP os. It's not a cube, just a workstation, but I'm happy to have it. I dumpster dove the workstation sometime around 1997, and my HS girlfriend's dad donated the KVM to me when he learned I obtained a workstation. He kept the cubes for himself; three previously employed at his now defunct typesetting company.
I have it displayed on the stairs to the basement of my software consulting firm. I nod at it every time I walk by.. and then ponder the chaos that would ensue if I plugged it into the internet.
I'm not Jobs' biggest fan, but we stand on the shoulders of giants.
Not a lot would happen because it doesn't have a DHCP client. You would need to open HostManager manually set up the interface.
I used a NeXT mono slab for 8-10 months while working at a NeXT reseller in the mid 1990s. It was a fantastic experience.
I should note that it runs "a patchy server" on boot.
Not a lot would happen if you plugged it into the internet, unless you happened across a bot that had some exploit for a 40 year old OS at the ready and thought it was worth the time. NeXTSTEP is well into the "secure through age" part of the bathtub curve.