This would be so useful.
I have a gap of about an inch or so above both my dishwasher and washing machine, underneath the work surface.
I shove baking trays, cutting boards, pizza trays, wire racks etc in those spaces, and it's handy - but smaller things get pushed to the back at times, and I have to use a ruler or something to pull them forwards (it's too narrow for my hands to go in). And it just looks a bit untidy.
If someone invented a sort of thin tray that's exactly the size of an appliance top, with a one-inch 'front' on it, or maybe even sides as well, that would be so handy for pulling things out, and also hiding them!
I was thinking of trying to bodge something up myself like that, but it would be a lot easier if someone had already invented it and sold them ready-made.