If you're using side-loading inner sleeves, simply insert the card sideways into the sleeve
Money for Nothing: Since you get money rewards based on the strength of encounters (and you could give yourself stuff for free via stealing, catching thrown items, or poaching monsters, and then there are things like the item duplication glitch), enough grinding means you can have more money than the entire GDP of Ivalice as early as Chapter One if you really care to be that ridiculously wealthy
All of the use cases are niche, but they aren't ones that never come up or anything
Scalpers that are driven by greed have wreaked havoc on a great hobby, creating a competitive environment to simply buy cards for a reasonable price
Code card for Pokemon TCG Live
Still, I think its likely that Stoneforge Mystic would be a feature of the format, and its hard for me to imagine Stoneforge Mystic making Modern a more diverse or more fun place