If the system you’re proposing would add a UUID field with a unique value either at new tiddler creation or during the import process, would this make it a good candidate for a plugin? While I understand why someone might want tiddler UUIDs, they (and any architecture needed to support them) would take up more space, as you say… and personally, I’d really like to avoid adding a new field I’ll never use to tens of thousands of tiddlers. (I even delete most of my created fields!)