This reminds me of an old thread on a random forum. Just when Sims 2 was released they were speculating what Sims 3 would look like.

Someone suggested that the next game will surely be in the source engine!

While your point is more realistic than that I still don’t think valve could pull this off in reasonable time. Translation for games is extremely hard to do right. I think if at all there will be another generation of decks before we see something like this.