The Desktop preview needs a "simulator" where we can change the size/resolution that we want to test on.

Example: I have a project designed for iPhone 6, with all art boards being for the iPhone 6, because that is what I'm testing on (my personal phone). I can plug my phone in and test the project on my phone. So, for iPhone 6, all is well. However, I am unable to test on any other devices because I do not own them, and do not want to redo all of my work, resizing them in a new file, for each and every device. At the least, I can ask a friend or two for their device for a few minutes to see what happens on it, or send them a weblink, but that does not help when they are busy, or tired of testing it for me, etc.

Solution 1: When I press the play/preview button, I should be able to switch between iPhone 4, 5, 6, 7, iPad, Safari, Chrome, etc, whatever...like you can do in Xcode for all the devices. Of course, only the popular ones would need to be listed. This way, a designer can get the design "correct" before sending out links, plugging in multiple devices, etc.

Solution 2: Have some sort of publish preview settings that resize things per device checked in the publish preview settings.

Solution 3: If the designer makes all the art boards in one project file, have the ability to create multiple testing links from that one file. I think this can currently be done in the publish preview settings, but its a lot of work to make custom art boards and redo all work, per device, making Solution 1 the better option.