Impact: Medium/High, ERC721 tokens won’t work without the metadata extension (name + symbol), but no tokens are loss. Likelyhood: Low, All tokens not implementing name and symbol will be impacted. This should be pretty rare because the two main "libraries" to create an ERC721, have those function in their main contract and not in the metadata extension. OZ since the version 3.0.0 and Solmate since their first production release. But as anyone can also implement their own ERC721 following the EIP, it deserves a medium.