Recognize x number of members each month on the front page using numbers from either like, trophy, points, activity, etc. etc. It'll encourage contribution.
Yup, and it would also be great if Admin/Mods can actually manually choose a member of the month (or year, or quarter of whatever period). We already do this on our site, but a system that supports this would be indeed welcome.
Having said that, I wonder what kind of functionality 'should' be core/what the developers envision as core functionality and what is better served as an third party plugin. Everybodies' wishes are different: in my case Xenforo can not be social enough.