Interesting. If they want to become a mainstream religion, in my humble opinion, I'd say:
A/ to become a normal Christian faith group in which its members are a happy AND proud to be JW's
Stop the practice of shunning. Stop brainwashing their members to believe that not being part of their loved one's lives is a good thing.
B/ to stop the haemorrhaging of its members.
Same way than in the first one, but growing the same way that other religions do, not by exploiting people and make them work for them for free.
Or there's the option of becoming a non-growing, yet, solid religious organization out of being a supportive, loving caring organization, not being there for the money as they are now.
Also, become professionals. If they want to have people make important life decisions, at least have a clue by having professional counselors, early child education people, mental health professional. That means that they have to completely change their "magic Jehovah" attitude that service or their Bible translation is the answer to everything.
There's a lot more they could do, but that's a good start.
C/ to rid themselves of being stigmatized a cult by Joe public and thus more appealing as a Christian organisation.
They are not being stigmatized as a cult. They are a cult. So this one is simple, just stop being a cult, and show it.