For modellers (model railways or model engineering), we often need to make two-sided chemical etching of brass sheets (with standard thickness of 0.3mm, 0.5mm, 1mm etc).

http://www.jimmcgeown.com/

The process itself (including the gerber file stage, and the etching stage) is very similar to the PCB manufacturing, except:
- sheetmetal etching only has two side to etch
- no vias, electroplating or printing on top of the sheetmetal.

So I guess the sheetmetal etching process is simpler than PCB manufacturing and uses the same etching equipment as PCB manufacturing, therefore I guess it would be relatively easy for seeedstudio to do sheetmetal etching without extra capital investment, but this would be an immense help for us modellers.