Also, there are power users, 'influencers', who are trying to cultivate an audience, often across multiple social networks, and they are looking for the ability

Also, there are power users, 'influencers', who are trying to cultivate an audience, often across multiple social networks, and they are looking for the ability to schedule posts ahead of time, and receive metrics and basic analytics on what sorts of impressions they reach. Products like this exist: search 'social media scheduling' or 'social media management'. I'm not convinced that your solution as your describe would be an effective competition to more full-featured tools, but at the right price point you may be able to attract customers who don't need all the features that those solutions provide.