The idea of thread is that it is basically IPv6 over Zigbee, in the form of 6LoWPAN which is an IPv6 stack optimized for low-power devices with an addressing, discovery, and routing mechanism designed to work well on mesh networks like Zigbee.

To some extent, Thread and Matter are direct replacements for Z-wave at different levels of the stack. There are some different pros/cons between the two though. The major advantage of 6LoWPAN is that it shares a lot of the design and implementation with existing network stacks and can be carried directly over IP networks. This is expected to make more complex 6LoWPAN topologies much easier to implement (e.g. 6LoWPAN traffic can be easily forwarded over the internet by a gateway). None of this is really anything that can't be done with Z-wave, but 6LoWPAN makes it easier by having a lot of common design and implementation with ubiquitous IP stacks. Matter itself has the major advantage of being a newer and higher-level design than Z-Wave which should result in more consistent interoperability of a wider range of devices.

Z-wave will probably remain superior for battery-powered sensors into the future, because Thread doesn't allow for the extremely aggressive sleep schedules (e.g. sleep mode for 18 hours at a time between supervisions for security sensors) that Z-Wave does... although we can of course debate how wise it is to only perform supervision every 18 hours, even if UL allows it for burglar alarms.