if we need 80%+ of support
for everything, how can we ever hope to make changes to the
fundamentals, like getting rid of wiki syntax in favor of rich text
editing, or implementing a better discussion system?
The issue there isn't community support, it's development. There is
work being done on the parser that might make implementing WYSIWYG
possible in the future, but I wouldn't expect it any time soon. Once
the feature is implemented, the community can decide whether to use it
or not, but it's really a personal choice, so I imagine the developers
would just implement it on Wikimedia sites unilaterally and let
individuals use it if they like.