IF SteemIt is viewed as an Alternate Reality Game, then tax liability may arise when there's a Capital Asset Gain (Losses are another story). The only thing the tax payer really has to decide is if SteemIt usage is for business or a hobby.
https://www.irs.gov/businesses/small-businesses-self-employed/tax-consequences-of-virtual-world-transactions
https://www.irs.gov/uac/is-your-hobby-a-for-profit-endeavor