We've devised a mechanism for writing tests of wiki in wiki which has enabled test driven development of the Wiki-21 reimplementation. We want to extend this method to new plugin development by authoring with non-existent types.
When plugin loading fails we render the failing item with a diagnostic button [Help]. It has been our intention that this page is otherwise healthy. This seems to have relapsed in some cases which should be repaired.
We don't offer TextEdit for items with a failed plugin load. This interferes with our convention of removing markup as the signal that an item should be deleted. We should offer this on double-click so that the unwanted plugin can be discarded and the test cases for future plugins can be refined.
We don't offer a user interface for entering novel item types. Editing the page json in .wiki is offers a crude and error prone path. A better alternative would be to use the Frame integration to construct items of the anticipated type, perhaps as part of a plugin development kit.