That is a very long story. The devs have been working on a plan to bring the two versions into alignment for many months and there have been some changes in the plan over that time. Now that we are finally caught up on patches, we're in the final phase, but they haven't announced exactly how that will work. I've got a thread going where I keep track of the progress which you can follow over here:
The devs are usually nice enough to update us in that thread as they work out their plans, but after getting burned with multiple delays from Sony & Microsoft before Christmas, they haven't said a lot about the exact plan beyond this point.
And here's the last and best explanation of the plan from a dev: