Let's inventory the other constraints.
1. Unawareness - The prime constraint in the BTC way is it being too technical. Major portion of the globe is still technical conservative and money over internet is still utopia.
2. Governments' intention - No country would like that its citizens use currency unregulated by it. This will make the country economically weak on international front until it accepts bitcoin as prime currency which none country gonna do ever.
3. Internal conflicts - The scaling issue has arisen the internal conflicts and who knows we gonna see more conflicts and constraints in bitcoin ecosystem in future.