Great update! Regarding I2P / Tor support: Dear devs, please post instructions on how to install ShadowCash on Tails 1.8, since it comes both with I2P and Tor already pre-installed and pre-configured.
My understanding is Tails has an option for "persistent volume" ... in which case it should work. I have not tested it though and it could certainly weaken the appeal of using Tails to begin with.
In reference to TOR/I2P .. you can run the wallet on a normal PC and point the Proxy (Tor) or SAM Bridge (I2P) to the Tails device.
On a side note, I2P works best when it has been running for a few hours (preferably days) ... so your best bet is to have a dedicated device which runs the I2P router and pointing the SAM Bridge connection from the Shadow wallet to it .. a RPI would be perfect for this and support the I2P network.