We would need time limits for that.

The easiest would be with users, but if we don't keep them these are wasted marketing resources.

Retention will vary from dApp to dApp, so I'm not sure we can easily measure retention globally, and make it relevant.

Price. If we are talking about growth based on real market demand, that's hard to measure or know the exact timing when it will happen. If we are talking about inducing the price growth ourselves, that may be or not achievable, depending who's on board, and it may turn into a pump and dump. But currently I think STEEM is on its way up on its own.