It will take some trials and errors from newer DApps on Tribes or SMT. Due to sheer number of attempts, one or few DApps can be a big hit that will bring millions of users who will require SP/RC to operate.

Users of that DApps might not be aware of the underlying Steem blockchain. DApp can provide necessary SP (e.g. 20 SP delegation) to new users to function in their DApps. In that case, that successful DApps will require millions of SP. The killer idea for that DApp is still to be seen: right now, @actifit, @steemhunt, @sprinterlands, @palnet, @steemleo, @dlike, @threespeak have good possibility.