Steemit is kind of like a ponzi but less scammy. At some point, when the whales start cashing out, the value of Steem will tank (just like a run on the bank scenario with MLM's, or perhaps upcoming with Tether).

But when and how fast that will happen is still TBD. I'd watch the # of new accounts being registered. When they start drying up, that's when you'll need to be first to the exists. Even the newbies are having a hard time earning due to the dilution of so many accounts. The easy days of a few $100 per post are gone unless you buy Steem power, but for that investment, might as well pick an alt or two.