Hi there... well, the old forums are run by Chucklefish (current mobile publisher of Stardew Valley). As you may know, they are a completely separate company from me. They won't be able to transfer users over to me because they have to maintain the privacy & consent of their users, who signed up for the Chucklefish forums, under their terms & conditions. I think there may be legal issues with that as well. And the data from those forums are inextricably tied together with user data, so a data migration is also impossible.
That being said, I encourage everyone to sign up for these new official forums and create new threads here with any useful information they have.