There are no limits in the world of Pokémon mods, whether they involve software (eg. ROM hacks) or hardware such as cartridges which Modified has delightfully demonstrated here. In the above video, they used a kilo of silver and made a Pokémon Silver cartridge out of it. And yes, it works.
This isn’t the first time someone has made a cartridge out of metal. In 2020, a Redditor called Ryn7321 posted two Gold and Silver cartridges made from aluminium (which, by the way, was more seen as more valuable than silver by Napoleon). And some more from Reddit here.