--- TEMPLATE BLOCKS
I would find it quite useful to be able to create "template blocks," which can then be inserted into a page like any other block. These could be great for creating modular templates for when you have similar pages but which require slightly different information.
With these, we could do things such as creating a single page of mini-profiles for NPCs that don't warrant their own pages. We could also modularly modify pages from existing templates, such as different blocks for cities, towns, etc on a preexisting location template, or elements that only some characters need on a preexisting character template (like divine powers and domains for gods, or PC-unique blocks).
These blocks may need to be their own special type of "page" which can contain only one block each, and account for blocks within blocks, like a table inside a layout.
--- SYNCHRONIZED BLOCKS
Another useful use of these: "synchronized blocks." With these, any time you edit the "root/master/parent" block, it updates all other instances of that block wherever it has been inserted in the project, including on templates. (This would be slightly different from synchronized articles.)
This would be great for information that might appear on multiple pages, such as lists or info boxes for things like factions, shops, gods, links to other articles, etc.
Synchronized blocks would probably warrant being stored in a separate tool folder, like templates, and they'd need to account for what happens if the inserted/child blocks are edited, perhaps by disabling the ability to.
--- Tagalong Feature
For both of these ideas, it would be useful if each of these blocks could index what pages contain them, and pages could index what blocks it contains, or at least synch'd ones, similar to tags.