Actually offering airdrops won't be very effective for Steemit, inc. Here are the reasons why:
1. Airdrops are meant for projects that are very new and offering free tokens is a way to get the project off the ground so that the first potential customers get started with the beta tests.
2. From the beginning of 2019, we will have SMT's. Several different projects would be offering their free SMT tokens. All the smart media tokens would be created by consolidating Steem tokens (just like ERC20 tokens are through Ethereum).
3. We also need to remember that Steemit is not alone now. Other players like Musing, DTube, Dlive, Dsound, etc. should all need to promote the steem blockchain.
Note: Airdrops might bring in few new customers but at this stage of Steemit, spending money on adverting is far more effective than airdrops,