Given progress to date and the fact Frontier are hiring more people, I'll bet it is sooner rather than later.
Well, I'm sure we all hope you are right.
I would not be at all surprised if Earth is the very last place we can land on. They have to do atmospheres, and thus weather, plus, I imagine, surface water. That is a big chunk of work. They also have to eventually do the flora and fauna generation and, for the fauna anyway, movement and behaviour. Another big lump of work. Then they have to do populated planets, with cities, and people and all that stuff. Only once they have done all that lot can they think of doing Earth. And because it is Earth, we will expect the animals to be 'right' and the ciries to be not only right, but in the right place, and so on, and so on.
However, we have certainly seen that FD want to do that sort of stuff 'right' from the effort they have put into the stellar forge, and the generated objects, as we are now seeing with the teasers for Horizons. Assuming they are still getting the sales they need (and the problem here is the quality of the game on top of the infrastructure is nothing like as good as that infrastructure), I certainly see DBOBE insisting that they do a good job, or not bother (shame they don't apply that to the game).