StarUML is just really slow for me.
This might come down to using web technologies for the program and me not using my best PC but it's still not slow and I think a computer that can run Photoshop without any hassle should be able to run a UML diagram software.
However, a usable performance would definitely be a killer feature to actually buy StarUML.

To define N-aray association between classes.

For documentation purposes it would be nice to be able to import an image file into a Note.

Specifically I want a UI Screen shot.

Implement C++ profile beside the existing UML standard profile

It's quite easy create a class, operation, atribute or role, but to describe the documentation, you need to access the lateral menu. This is inducing users to avoid to document. It should there a easy way to do it, like a shortcut, or even one of those little icons which you already use for another task.

For god sake! I can't believe that nobody mention this...
Who is designing and app for bloody diagrams without an option to easily copy styles between graphical elements... (like f...g color or font...)
Morons!

Just like in programs like Photoshop or Sketch - pressing and holding spacebar puts the program to "dragging" mode where you only can drag the canvas around instead of its elements.

As an enterprise architect, I use ArchiMate for high level modelling and UML for more detailed modelling. It would be great if StarUML could add ArchiMate support!

Add more control on the details of the generated HTML report.
Not all stakeholder are interested on all the details ...
Some may need only outlines, description and diagrams
while others may want to see all the details
and there are others in between.
Giving control over the details of the generated report will help to satisfy all stakeholders types.

A class attribute (or relationship label) with, for instance, a dash is not accepted when editing within a diagram. However, the same works within the "Properties" window on the right. (Also, when trying to remove a relationship label within the diagram by deleting the text which was currently there, it is not possible within the diagram and is possible within the "Properties".)

I would like to have the ability to group elements.
An Auto-Group function would be great too. E.g. classes assigned to a package should also be moved when moving the package because the classes are automatically grouped with the package.

Please add support for annotations at Class, field and method level.

Please add Git Support to the Editor so it's possible to check in the Diagrams into a Git repository.

I am using the MarkDown extension and like to preview the HTML docs generated frequently. But each time I have to browse to the directory where I want them saved. This would be great if it simply remembered where I chose last time.

It would be nice if StarUML could support modelling of Requirements and Test. I like the approach taken by Visual Paradigmen 11.2(http://www.visual-paradigm.com/features/uml-and-sysml-modeling/) by supporting "SysML requirement diagram". I tried to emulate it in StarUML 1 with an own model but it isn't quite practicable. If this feature would be voted, please take attention of text-wrapping for the elements and give a possibility to define own values (e.g. for risk). If it's not to much, the fields of the requirement-template should be definable by the user.

PHP Code Generator and reverse engineering

There should be an option to export diagrams with text documentation. For example use cases diagram with Markdown documentation for each element.

In "Explorer" moving things to be sub items of diagrams seems to be a single item at a time experience (unless i missed anything.) Would save time to be able to control-click or shift-click to select multiple items in explorer to move.

add sysml support to fully features for SA