One thing I have long hoped for is a kind of symbol that even when expanded (since you need to edit the symbol eventually for copy or what-have-you) can be changed globally from the source symbol. This way an instance of a symbol can be edited in a single place despite having things like custom text, or dimensions (particularly helpful for menus and buttons). Symbols, by nature need to be nested for complex interactions so this would be great as well.

Master elements (like in Axure RP) og Symbols (like in Sketch). Without this feature we won't be able to switch to Adobe XD.

It would be nice to have an area dedicated to hold custom objects. Since these object are reusable, letting XD organize them and have quick access would make prototyping even faster. Currently I am putting them off to the side of the art board for future reuse.

The one thing I would love is the ability (option) to add a prototype link to a symbol, that stays with it by default, e.g. a menu button (linking to the menu art board), then if that symbol is changed the prototype link is retained. Any duplication within art boards of the aforementioned menu button (which happens a lot) means the prototype link does not need relinking over and over again. I have found that this repetition aside form being tedious and feeling like a waste of my time also creates a tendency to miss the repeated instances on some artboards and thus breaks the prototype which is equally frustrating. ‘One symbol and prototype link to rule them all!’

Got that in sketch, that's one of the things stopping from using Xd

I would definitely appreciate to be able to even nest symbols, like it's already possible in Illustrator. Developing this into fully fledged components (defining constraints and extracting variables to easily create variations of a symbol, very similar to how Flash components worked) would be killer.

I 100% agree with the below comment almost entirely, except I have started using XD. It is such a pain to update every instance of my 'menu' button with a prototype link to the same art board. It should be linked once and then every instance of that item should embody the same prototype linkage for starters.

Just completing the idea ... make a tool called "clone", where all cloned object "menu, etc" will change together

One feature I most need, is to repeat the menu bar in all windows... than when I change the name, color, design, anything on that menu, it will repeated for all menus at my design. So I create a main menu, and if I change any name, vector drawing or image in those "brothers" menu, will repeat at all menu bar.

Not having symbols or the ability to insert or place a single source repeated element like a header or footer (so that I have one editable source that I can update across all artboards) is the #1 thing keeping me from being able to use XD. I was really excited about XD until I realized that limitation!

I can't adopt XD (and I want to) until this feature is added. It slows down the workflow without it.

In Illustrator I can have another Illustrator file or symbol source for a header, footer, icons or other repeated page elements, update that single referenced file and it updates across all artboards where it is used.

Get this added soon!

The ability to build a custom object library: things that you can easily import like buttons, forms, layouts, etc. It would be great also to be able to work on each object individually. For example, one place to create / edit this table (see attachment), and then, the result reflects on all the same-class tables across the project

Scrolled through 6 pages to find someone who would mention custom templates/smart objects. Seems like it would fit right in with things like the repeat grid to create designs quickly. Updating menus across all artboards when editing one (by linking them or making them a basic template element) when you've made a small change would be great.

Smart objects or symbols that are able to hold multiple states. Build on button, icon, module, navigation and display different states as it appears on different screens. Currently doing this in photoshop with smart object, layer comps, and the properties panel view layer comps drop down.

Related feature is having a styles palette so that multiple components could share the same custom named style. Changing the style would affect all elements on the screen with that style.

Absolutely essential. I end up having multiple instances of the same icons, elements, groups and entire blocks across screens. Then should I decide to change styling I have to go through each one and repeat the same operation over and over again.

I would love to see symbols in this app. It's important to be able to edit and create symbols in context for me. Sketch has recently removed the ability to do this with a recent update. It's worth looking at their facebook and medium blog to see how the community has responded. Some interesting insights to be gathered here.

FEATURE-UNDER-REVIEW? Really?
I'm sorry, but as previously stated by many people on multiple threads, this feature or one like it is ABSOLUTELY essential in making XD a competitor in the industry (efficiency wise). It's currently slowing my workflow down 10 fold as I was shocked to find this wasn't a beta launch feature that is included across the board on all similar products.

Symbols, yes, as many others have stated, would be a big productivity boost. Especially if they could work like the CC Library in the other apps (i.e. being able to drag a symbol from a list into the artboard).

But it would also be a boost if I were able to place symbols into an artboard and set them to appear in all artboards of the same size.

For example, if I'm designing a website, the navigation menu will likely stay the same on every page. If I could create it once and then set it to appear on the other pages, that would be a lot easier than having to copy and paste the group over and over again.

And of course, being able to update one symbol and have it sync to all of them is a must as well.

On top of that, I suggest to save links assigned to each symbol.

For example1:
You create a button with a link to another artboard (in Prototype mode). Then if you copy the button to another artboard (in Design mode) link remains assigned to this button.

Example 2:
You have a "menu bar" symbol with several menu items in it and with links assigned to each item. When you change a link for any of the menu items, the link changes in all symbol instances in the project.

Surprised this isn't voted higher. Without this feature, I think photoshop still edges out XD for being able to design UI systems. For example, a navigation bar.