Back in about 2015, Sigma Designs Inc. produced a hardware Ethernet to Z-Wave device for distributed hotel room control with a software stack called Z/IP. Basically PoE + a box for (say) two hotel suites (where the 100+ node Z-Wave network limit would be exceeded across the building).
Here’s a contemporary report and a Z/IP ZIPR gateway hardware picture:
The openHAB project looked at it (I still have many of the original tech documentation PDFs), but the hardware only worked with the proprietary Z-Wave software Z/IP API stack so it went nowhere. At the time, the hardware was available from suppliers like Farnell, but I’ve not seen any reference to it for a long time.
For me, extending your existing Z-Wave mesh is preferable to creating another island. With more IPv6 friendly alternatives like Thread on the horizon, unfortunately don’t see the point!
(For reference, I have many tens of Z-Wave devices in production use.)