Cool, someone else is doing it. I always wanted a metal DMG (after seeing a steampunk DMG, i think it was thretis?), and wanted to do this project, but hadn't the slightest where to start.
I wanted to do a Metal DMG with either Embossed or an Impression of the Nintendo Logo, Start, Select, along with "A" and "B" (with matching metal battery cover ). . .. Maybe metal Buttons and D - Pad, if it's functional without shortage,
And to find a metal smith that could do the case with this type of Treading. 
With the ASM Silver or Chrome Front covers.
(http://asmretro.com/diy-gear/screen-cov … reen-cover)
mmm, The only thing I would have to had all the Holes and everything sketched out before the mold, because I would like it to have some modded features too. Backlight, prosound, power light, maybe more, but yeah. It's my to do list.
Let me know how you're Case is coming out, and if you're doing more. I think it's a good idea! :) maybe an additional coating to protect from sweaty hands?