The idea of putting major changes to player votes is a good one. You
might poll the current player base about what level of support they feel
a significant change ought to get.
By doing this now, you get a figure you can use--take the average and
then err on the conservative side a bit, and then TELL the players what
the number is, so that they know what kind of popular support an idea
needs before you'll make a radical change.
As a ballpark, I think 80% is a good figure. If that many are willing to
support it, relatively few are likely to be incensed by it.