Take a role playing game as example in which players are allowed to create any number of characters (each one defined by an ERC-721 token). What would be the consequences of having more than 10 billions of characters created? It's just a matter of the amount of gas players would require to create new characters?
ERC721 gas costs are scale-invariant.
It's just a matter of the amount of gas players would require to create new characters?
Yes. That is correct. It is financially constrained.
An important heuristic is to avoid introducing anything in your contracts that would increase in cost in proportion to scale. In case that sounds cryptic: https://blog.b9lab.com/getting-loopy-with-solidity-1d51794622ad
Beyond the contracts themselves, client-side processes could be impacted by the size of arrays, etc., so keep that in mind, but generally you would be able to use familiar techniques to address performance concerns.
Hope it helps.
I demonstrated at NFT.nyc in March this year a technique to create NF token with O(1) cost. In other words, make as many as you want.
This is the same technique as used in Su Squares and you can see the slides at http://nft.life