The challenge for the community is to simplify the map creation process for newbies. OSM for dummies still has to be invented.
But the growth of OSM will also come from data donation by public or private third parties as well as imports from public datasets. The TIGER data from the US Census Bureau or the cadaster data from the French ministry of Finance are two examples that have contributed to accelerate the map overage and its depth in these geographies.
The Open Data movement is creating a wave of new public datasets (unfortunately not all of good quality) that can be added to the map.