I personally don't think they will ever have God explicitly show up. He's God--literally the answer to every single problem, forever. Once He appears, it's over, so maybe at the very end of the series finale, we'll get a glimpse, but even then I doubt it.
On the other hand, there is no necessity for God to show up yet, since the episode clearly lays out that the hands of God can only be used by God's chosen, which is why Lucifer couldn't tap into his piece's full potential. I doubt any angel could, actually. Watch, it's going to be something contrived, like God's chosen are humans, or something.
And it's also too bad about Death. I wonder if he could have done something about Amara (even though he already said he couldn't last season).