Almost all of the stuff that has been changed are additions. For the most part OH 3 is just OH 2 with stuff added. The primary exceptions are:
- PaperUI is replaced with MainUI
- A few breaking changes in rules, namely executeCommandLine and the replacement of Joda DateTime with ZonedDateTime
- System started triggered rule won’t run when you merely save a .rules file but only when the system has started (i.e. on a restart of OH).
- there are various breaking changes and changes in behavior in individual bindings but not the Zwave binding.
- there is a different version of the Helper Libraries that need to be used if rules are written in Jython.
Pretty much everything else that is different is handled by the upgrade script (i.e. apt if running on an RPi). Of course how much the above changes impact you will vary from user to user. Some users won’t notice at all, other will need to modify each and every one of their rules.
Many, if not most of the people who have been around for a bit and are running OH 3 upgraded in this way.
But obviously that means that once upgraded your config won’t take advantage of any of the new OH 3 stuff, but who would expect that in the first place?
This is not to say that I’m advocating that you upgrade, just that the option to upgrade is very feasible and reasonable.
There is a Remote openHAB add-on that will link the two instances.
If you are running a recent milestone of OH 3.2 (M3 or later I think) there is the Marketplace where you can install the MQTT Event Bus rule templates (see Marketplace MQTT Event Bus). Of course you can just use the code to manually create rules also but why go through that if you can just install the template and instantiate the rules, no code involved.
If you have moved to HABApp there is an MQTT Event Bus implementation built on that too, though it looks way more complicated to install and configure.
You can use socat and ser2net to run your zwave controller and connect it to your one OH 3 instance over the network.