Mmmm.... Each dimension means less when considered individually - particularly the combined thickness and depth as those create the cross sectional area - those two combined define how small a pocket it can 'fit' in.
The existing Pandora's thickness (29.25mm) and depth (83.48mm) create a cross-sectional volume of 2441.79 mm^2. I consider this to be a critical maximum - any larger and it no longer fits in a shirt pocket - which is relevant if you're a guy (me) wearing dress shirts (me) on long flights (me) listening to music on your Pandora (me) while eating whatever the airlines are trying to pass off as a snack meal on the fold-out table. So, yes this is a personal thing that I'd like the Pyra to not exceed that cross sectional area.
So...
If it is going to grow in depth, then it needs to get a bit thinner.
Width is far more forgiving. The current Pandora is 140.29mm wide. Adding width is easy - to a point. The restriction winds up being, "How wide can the device be and still be thumb-typable? I.e. how wide can it be and still let people with smallish hands use it properly? I have big hands. I would be fine with it being upwards of 16cm (160mm) wide.
Maybe re-state the poll? What we really need is, "What is the maximum -MeasurementDimension- that you would accept?" and "What is the minimum -MeasurementDimension- that you would accept?"
However, it really all comes down to:
What is the smallest size that the lid can be and still fit around the screen? That dictates the width and depth of the device.
Once we know the lid dimensions - dictated by the screen dimensions - then the thickness is, "as thin as possible with the hardware that has to be in it."