If the Watchtower really wants to move more mainstream they need to take a lesson from Evangelicals in the United States. They seem to say there are "Essential Beliefs". A handful of core beliefs that are necessary to be considered true Christians. These beliefs set them apart from everyone else and mark them as "authentic". The "non-essentials" are basically up to your conscience and not emphasized.
I see this in books, churches and so forth in the last few years. Perhaps in response to controversies in the Evangelical world I don't know.
I really think this is what the Watchtower needs to move towards. It would still set them apart from other Christians (the non-trinitarian view) but many would find it reasonable. I will list some as a possible example:
1. Father, Son, Spirit separate (current belief and non-trinitarian)
2. Soul is the body (current view)
3. Hell is the grave
4. Resurrection at the end of time for all in the grave
5. 144,000 is symbolic
6. We are in a last day period since Pentecost
Birthdays, blood, shunning is a personal matter although counsel to those not following matters of sexual morality (conservative view) will still take place.
This is just a quick list, what would you think might be considered "essential" to a more mainstream Watchtower?