It can't be currently implemented on every node, because Bitcoin nodes don't talk end-to-end encrypted, and end-to-end encryption is necessary to insure anonymity. Such feature would require change in the way they communicate. It'd be better if, instead of changing Bitcoin Core, you just installed an addon.

I don't find utility. Stamping your network address on the blockchain means it won't be altered, but that's all. It doesn't provide any (other) benefit; pretty much the opposite, it makes things work more costly. Tor nodes can't change your network address either, because all they see is encrypted messages. As long as you own the private key of the onion address, you do get censorship resistance.