They're basically already doing all of these in some form or another.<p>1. They'd never describe it as this, but sign up as an advertiser and you essentially get all of this.<p>2. They're essentially doing this with their new interest based targeting for advertisers, i.e. mining users for interests and then letting advertising pay to target those interests.<p>3. Promoted tweets all the way. While they don't have follower count as a targeting vector yet, they do have everything from device and location, to gender and interests, to @handles and time of day.