I spend a lot of time when I'm designing a new screen for a mobile app.
Just to put a button in the right position, I need to "calculate aprox" the coordinates, compile (3 mins in my old computer), launch in the emulator or device and navigate to the right screen to see the button.
In total, for each error I have, I spend over 5 mins waiting to see it. Do it 12 times and I waste 1 hour just waiting, instead of working.
It will be REALLY good to have a "player", "viewer" or something similar just to see how will appear the objects in the screen "aproximately". Do not need to be an editor, just a "viewer".
If you consider this idea, this could be a small roadmap:
1. Do a very basic viewer: provide the alloy (xml+tss) file and "represent" it graphically in a standard "medium density" (or 160dpi).
2. Be able to configure the screen resolution to see how the interface appear in different resolutions.
I don't know if this would be hard to do or not, but I launch the idea.