This is a good one :)
Build some decent service, have it used by human rights activists, and any sufficiently oppressive government will advertize (the same way) it for free.
Heroku certainly is a huge time saver. And you certainly can build high traffic apps if you use a stateless and reactive frameworks like Play, Vert.x or Node.js. Even within the free limits.
What do you think of this idea: developing billing plans as functional code (sets of functions), managing them in Git (changes, versions, effective dates) as any source code, treating stored account data as immutable results of transactions (making account data available for any given moment)?