Here's a link that talks about down sizing the engine.
I know it's just one link but i've read a couple of others and it still talks about down sizing the engine to 4cyn turbo.
I'm surprised nissan hasn't used DI for the 370Z yet. Other than having minor exterior changes over the yrs and price creeping up and haven't been able to have the same success as the 350z (probably due to the economy), it seems they will down size and make it cheaper.
2015 Nissan Z May Be Lighter, Leaner