It's not clear from what I have seen exactly what the Zcash integration as you call it will involve. Let's see what they do first.

I thought you were suggesting that Steemit should run on ethereum which would be pretty much unfeasible.

Some kind of connection between the different networks might be possible but I don't know enough about the actual graphene protocol to know for sure.

I do seem to remember Peerplays (another graphene project) suggesting this during the DAO.

Hopefully someone with more knowledge can fill you in.