The 3-hour block is vilified by some members, and it is the one thing that many members say they would change about the Church, but it often is that same group who blasts the Church for not educating its members enough on historical and doctrinal issues. So, on one hand, the Church needs to do much more to explain and teach difficult doctrine, but, on the other hand, the Church needs to reduce the amount of time members spend in meetings being taught history and doctrine. Can you see why I end up scratching my head in frustration at times?
I would rather tackle the instruction during those three hours and make it as good as it can be first, then evaluate if the actual amount of time can be reduced. Does anyone know what the Brethren have identified as the greatest "failure" of the three hour block? It is that the block was consolidated to allow families to spend more time on the Sabbath and throughout the week together as a family - but most members haven't used it to accomplish that objective. Rather, they have maintained their previous practices on Sunday and just added other activities during the week to replace the church meetings they used to attend.
How can you tell if something should be eliminated unless you've run it the way it was intended to be run? If you are going to eliminate something, what would you emphasize in its place? The main thing I would change is an individual recognition among the membership of what is good, what is better and what is best. If everyone took that responsibility seriously and only focused on the "best" things, much of the "good" simply would die away. Until the members take that responsibility on their own, however, I don't want the Church to eliminate things on a widespread level and "limit my choices" about what I can do.
So I say, don't ask the Church to change first or primarily; change yourself and live whatever you feel is best, according to the dictates of your own conscience. Pick and choose which non-Sunday meetings and activities to attend, how much to pay in Fast Offerings, how often to attend the temple, how to serve others in the community and/or world, etc. Take responsibility for your own decisions, ironically, as the Church constantly requests.
I'm trying hard to change myself, regardless of how the Church changes. Ultimately, I take responsibility for how I construct my own life by what I prioritize, and getting others to do the same (no matter what the individual outcome) would be the one thing I would "change about the church".