100% agree that viable is context driven, but I kind of disagree with your example. If you want to compete with an established player, focus on the differentiating factor that you think is game-changing rather than competing on features, otherwise you'll never win. The early adopters that you want to court will be excited by what's different, not by a clone of something that already exists. By the time the product is ready for the prime time it will need those features, but by then the bleeding edge early adopters will have moved on to the next new thing.

However, in cases like healthcare or finance, or certain B2B applications, viable may entail a much more mature product.