No one knows when Carlos will return, but it's most likely he'll return after he has finished Beta 6.
He's doing a lot to revamp things on his hack. So by the time he returns, he'll post the new beta of Shiny Gold. And please don't ask when, 'cause I don't know.
It might take some time, but it will eventually pay off. Besides that, he has Uni, Work and all that. So I don't think he'll be back 'till probably next year or so.