Recently, MoneroWorld added a mining port for I2P. Are there any disadvantages to mining with I2P instead of connecting to the pool directly? Eg: will it be sgnificantly harder to submit shares? Is the connection less reliable?
There is significant (and variable) lag in the i2p network - try visiting any i2p website. As mentioned on MoneroWorld.com, this could cause an increase in stale shares (you submit a solution for a block that already has been solved).
i2p lag will only decrease if more and more people run i2p nodes. (and by i2p nodes I mean running the i2p server).