Crossovers are fine. That's not the issue being noted here. The problem is that people imagine generic items are cross compatible within many games, but that just doesn't work. If you want to make a crossover version of the master sword in minecraft, sure, that's cool. If you want to somehow import the data and just assume some sort of parser will get the properties and the look and feel right, you're going to have a shit time. And then still you'd be better off on a centralized setting.