Alright. Why isn't this a commercial product? Maybe it is and I just didn't see it.
Usually you see guys on YouTube video justifying the value of their Harbor Freight (or other brand of nibbler) by cutting sheets held floppily in the air or off the floor. That seemed to me that unless you are particularly well coordinated or had a lot of practice to be a "rough" operation. Now I'm pretty good with a table. I can do carving with one if I have to. I think that's partly because I can have two hands on the work piece if need be, but also because the work is fully supported. Why not with a nibbler?
Ideally the punching action should be reverse for a table mounted unit, but if its made height adjustable I see no reason it wouldn't work with the current range of power nibblers on the market.
I'm going to make one. Small 8x12 table for now. Probably with a heavy angle on one edge to mount in a vise, but if it works out well I have considered making a table as a leaf attachment for my table saw to support even large stock. (Warning! Wood working content.) I already have a leaf extension for my one of my routers that works out better than a small router table or even a small shaper table.
The only other thing I can think of to make it easier to use and manipulate would be a foot valve for air or a foot switch for electric.