Good news from Trezor Support!
We are testing and optimizing ZCash support on our beta version of myTREZOR web wallet - beta.mytrezor.com
You need to change backend server to ZCash (please see and select this option below on the website, where you can change currencies) and then in “Currency backend” choose - Waterhole.io
I sent some of my hard earned ZEC (transparent address) to my Trezor device and it worked flawlessly! Please note that this is still in beta