Might be a fun project if there's nothing out there already (I assume you've searched), check out text steganography if you haven't:
https://ctf.support/...
https://www.fourmilab.ch/javascrypt/stego.html

I don't use i2p but:
http://wizardcasa.i2p/
http://wizardbloat.i2p/
and clubcyberia.i2p used to work, but seems to be down rn