I disagree. It’s just as easy to backup /var/lib/openhab2/jsondb/org.eclipse.smarthome.core.items.Item.json as it is to backup /etc/openhab2/items/*. It’s stored in plain text just like .items files so you can use git or the source control of your choice to track changes and such. openhab-cli backup also backs up everything in the JSONDB, as does Amanda or any other automated backup system. And unlike .items files, OH generates backups of the JSONDB files automatically (/var/lib/openhab2/jsondb/backups) whenever you make a change. Thus, it’s actually even easier to revert a bad edit than with .items files because the older copies are created for you automatically. And because the editing of the JSONDB isn’t usually done directly, it’s much more difficult to make a bad edit as the core will prevent anything syntatically incorrect from ever being written in the first place.
The only thing that is harder is manually editing them with a text editor, which is reason enough to stick to .items files. But backup and restore is not a compelling reason as it’s not harder than it is for .items files and in some ways superior.
It largely depends. If you have 1.x version bindings I don’t know if it is known yet whether the binding configs will still work when you migrate to Managed Items. They load faster than .items files and I don’t think they are as prone to experiencing the startup timing issues you often see (e.g. Rules start running before all the Items are loaded). Indeed you will have the ability to modify the Items through PaperUI and future UIs.
When you go into more esoteric stuff, when you have Managed Items if you are using Item metadata in Rules (only possible through NGRE) the metadata will persist across OH restarts. Any dynamically created metadata gets wiped out for Items loaded from .items files. See Design Pattern: Using Item Metadata as an Alternative to Several DPs for details.