The problem with suggesting feature's for any particular site is that the feature is evaluated in the full spectrum of SO-family sites. "Can we get X," one user inquires. "No, that wouldn't work right on Y and Z," another replies.
Is the option open for Meta-exclusive Features, and maybe another set of features that are geared towards the type of activity on SF, or SU? Each of the SO sites have similarities, but they also have their differences.
Perhaps if StackExchange had a nice API, and features could be developed and plugged-in as modules for each individual site?