>>8697>I2P does this if memory serves me right
It doesn't and it can't. Tor, I2P and any other low-latency network is vulnerable to correlation attacks. The only way to get around this is to add a random delay after a node receives packets to when it sends them (but this adds latency.) Otherwise an adversary can look at packets going in and packets going out and tell who is sending to who.
Tor and I2P do try to obfuscate, such as reordering packets and using fixed "cell" sizes. The adversary sees something like 1 KB go in, 1 KB go in, 1 KB go out, 1 KB go out. They don't know which of the 1 KB in the input went to which output. Over a long enough period, it may still be possible to correlate the packets going in and out to deanonymize you.
This is why mixmaster nodes add random delays between receiving and sending messages. It can take up to 48 hours for the message to get through, so people won't use it for web browsing, like they do with Tor.