Biggest issue with some 'use your item as an avatar in any game' is that doing cross-engine models is hard, and pretty much impossible if you want the model itself to be immutable, lest it break with some engine update rendering it useless. The only in game item thing that really works is when the game code has a texture algorithm (like CS:GO skin variants/wear levels) and uses the immutable nft data to calculate their unique item texture.