Give individuals powers once reserved for masses
Here's a common trajectory:
1. Something is so expensive that groups (or even an entire government) have to share them. Think about mainframe computers in the Sixties.
2. The price comes down until a committed individual can own one. Think homebrew computers in the Seventies. The "average" person wouldn't own one, but the dedicated geek-hobbyist would.
3. The price comes down until the average individual can own one. Think PCs in the Eighties.
4. The price comes down until the average person owns dozens. PCs, game consoles, MP3 players, GPS navigators, laptops, embedded processors in toasters and cars. An average person may have half a dozen devices that once were considered computers.
Along the way, the product first gains broader and broader functionality, then becomes more specific and dedicated.
Telephones, radios and televisions all followed the same trajectory. You would probably call these moderately successful products.
So: find something so expensive that groups have to purchase and share it. Make it cheap enough for a private individual.
Another Path to a Killer Product