This feature needs to be a high priority. I want to use XD, but without single referenced, master items, if I need to make changes in iterations, that is a huge time effort across many, multiple artboards. Please get this implemented soon!

At first mechanic like smart object in PS would be nice (another example is master object in Axure RP). It's painful to change headers in 12+ screens.

1. Global pinned header.

2. Global pinned element, e.g. a logo.

3. Non-global pinned element.

4. Pinned panel e.g. a menu UI; top, right, left or base.

5. Pinned panel that slides from off-canvas; top, right, left or base.

6. If scroll is a function: Trigger a pinned element on scroll to dynamically change; e.g. menu changes from a large header to small header with new or removed content.

Have a tap bar (Navigation) that does not have any transitions on it when you are in prototype mode.

Therefore it is constantly there and does not slide in and out with Art board transitions.

Additionally I need the ability to have every page display a common legend bar with a back button (back to parent screen) as well as a button to reveal / call up the top level navigation.

The usage I need for this is a persistent top level navigation that can be accessed from anywhere within the app.

Stateful symbols would be ideal. Define a symbol in the project, if the symbol has multiple states (such as a tabbed navigation element) then you could also define states (like Layer Comps in PS) and when placing a symbol on an artboard, you should choose the state of the symbol on that screen.

behaviour of an master artboard with styles and grid would be great. Integration of symbols or pinned objects like indeed navigation would be also great. In every screen you must be able to override the items if you like to...

As a designer I want to create one editable header navigation instance and repeat that across all pages to allow very fast flow and navigation management. Similar to photoshops smart object except with links tied to specific art boards.

+1 for mimicking Illustrator 'symbols' OR Photoshop 'smart objects'
ie. Yep to master objects and instances of that object

-1 for mimicking InDesign 'master pages'
ie. Nope to master pages with instances of that page

"Pinned Object" sounds a lot like the "Pin to Browser" feature in Axure.
As a designer creating a prototype I want to have an element such as a global navigation element showing across artboards and not scrolling while the rest of the elements in the dartboard move.

Master artboards, master components, master pages. All of these things have one thing in common, objects or templates with global effect. Being able to change a component on a single master page/artboard means that anything with a similar layout would be easily changed across a flow. Additionally, allowing for nested master objects and master templates within templates allow for core templates and objects to created that have a wider spread while having modifications made for flows with narrower use cases yet these cases need to be just as "global" as others. As for how it applies to prototypes, this means that once you set both designs and interactions in these master elements, you won't need to repeat existing animations, interactions and modes of operation.

As a designer, I would like to have a master artboard to have an element on all artboards in Design mode as well as in Prototype mode but with an extra feature that will include a common interaction that will be placed for all artboards.

For example, I would like my main navigation to be sticky and decrease in size as the user scrolls down past 300px in length of the site. This can be done by clicking on that element on the master artboard in Prototype mode and have an option to make it sticky, and drag the wire down to 300px on the page which then you can manually or automatically decrease the height/size of the main navigation. This should also automatically make the navigation go back to original state as the user scrolls back up the page (it should detect Point A to Point B and Point B to Point A so to speak).

Just some ideas to throw out there because I completely agree to have master artboards.

Agree, for my use case this can also be applied to how Flash used to have "symbols" and or "smart objects" in illustrator, the ability to have an object, group of objects be created and named accordingly and be able to be editable globally with just one edit to the master object and have this change be applied to all instances that this object is being used within a prototype.

Would it be possible to have a layer-type feature just for the pages? It would go a long way in keeping the prototype organized in design mode.

Agree with everyone here. Making global changes to common elements would be as handy as the repeat grid. Hopefully it could also mean that they could sit 'above' transitions too, so you aren't sliding the same navigation over the top for example.

Fixing regions can be as simple as selecting a region with a selection tool (drawing a box around it) and being able to designate the region as fixed, then linking the fixed region to all the artboards in which it needs to remain fixed (similar to how XD works when linking one artboard to another).

Similar to InDesign, I agree. Including command-clicking an master-artboard item on a regular artboard would unlink it. That way you could locally modify it.

I would think this would function the same way master pages work in InDesign or Muse. Master items, by their definition, are going to function the same way regardless of which screen you're on (think main navigation; buttons along the bottom for an iOS app or links across the top for a web page). I would setup my global items on a master artboard and whatever actions I attach to this global item would work the same way on whatever regular artboard they were used on. If I want to edit the actions of a global item I would need to go to the master artboard they originated from. I don't know if t's absolutely necessary but allowing master artboards to be based on one another like they can InDesign could make things easier for more complicated situations. Allowing global items to be unlocked from the master, similar to InDesign, might also be useful but I can't think of any situation off the top of my head.

I would suggest this just follows the pattern of symbols in Illustrator. For example, add a logo to an art board, then make it a 'symbol', every instance of that symbol across all art boards now can be changed with just one tweak to the symbol.

One ring to rule them all!