I think two things need to be true for a “feature” to be able to mature into a full fledged company/startup: 1. People need to be willing to pay for it. 2. Other companies shouldn’t be able to replicate it easily and put you out of business overnight within a single release.

Part 2 is especially important if you’re building or extending functionality on top of a platform. An example might be the old swipe-to-touch keyboards on iOS. Once Apple built them natively, game over.