Upcoming developments
Some of the ongoing developments are currently funded by the NLNet foundation. But other major developments are also planned.
Cross-referencing with external data sources
Flag differences between OSM and other business or OpenData data sources.
External quality rules
Validate changes using external quality rules (JOSM validator, Osmose-QA, etc.)
Contributor reputation
Take into account the "reputation" of contributors (beginner, flagged for bad contributions, statistical analyses) and changesets discussions.
Support equivalent tagging
Sometimes OpenStreetMap provides multiple tagging schemes for the same concept, such as address vs. contact tags or the different ways of mapping cycle paths. You may care about these features without caring how they are technically represented in OpenStreetMap.