Your proposal is a terrible idea, because Twitter should be paying those that genuinely attract an audience, not vice versa, since those people can always switch. Popular people will be popular anywhere. E.g. Linus Tolvards has a big and active audience on Google+, even though it is in general a ghost town.
Essentially a company / influencer marketplace.
They are the ones with the perfect data insight.
This combined w/ a "show ad to people who follow person N (and alike) might be a very strong ad format only they (and instagram, snapchat) can provide
Twitter's problem is that their ads don't work very well (compared to Google and FB), and their audience isn't growing.
Both of these things are solvable.
It isn't at all clear why people think there needs to be a new model. Advertising has worked well for hundreds of years (newspapers/radio/tv/internet) but it needs an audience. Twitter nearly has this.
Actually monetising a twitter account directly is a risky business, as it could easily drive down quality.
The FREE! model only works out when you can sell your users' attention. Twitter has proven that it can't do that -- for whatever reason, user attention on Twitter is not worth what it's worth on Facebook or Google and they can't make a profit from it. So they need another way to monetize, and IMO that should be the tried and true "make people pay for what they use".