According to Milviz, the plan is to "to add v4 functionality to all the aircraft that currently function in v2 and v3, starting with the newest and working backwards".
There's not timeline yet as "Each sim will require a different approach [...]". Milviz cannot foresee the difficulty of the different models so they cannot do a proper planning and release plan.
We'll have to wait and see but, at least, we know they are working on it. We will provide more news as we get them.