They could become more mainstream and still have different interpretations. There are many offshoots of the Miller and Russell-led denominations that are more mainstream than the JWs.
The biggest hurdle would be letting go of the "no part of this world" interpretation where they use that phrase to limit birthdays, holidays, and (most importantly) basic daily social interaction. The WTS has frequently promoted the idea that JWs cannot have friendships with 'wordly' people, and that they should even be circumspect around non-believing family members. Reversing that would be terrific, but might also be a bit of a shock to many rank-and-file members.
Still, I think it's the best path forward.