I noticed that you mentioned I2P and not Tor. Personally I believe that Tor has fundamental advantages over I2P. I believe that one of the greatest advantages of Tor is how much choice it gives to the people who participate in the network. Someone can use Tor without relaying other people's traffic, and node operators can opt in or out of being an exit node, even picking and choosing what kind of traffic and clearnet destinations one will allow the user to visit through you.
Not every user has the same values or OpSec. Some people live in countries where running a Tor node is illegal, even if they can't know what encrypted traffic they are relaying. I believe that I2P's choice to have everyone relay other people's traffic is a big problem.
Also, the small number of relays that allow for browsing the clearnet is a problem.
What do you think?