That's also what I thought when I started developing it: I can imagine myself reading such a site when it's established and active, but building one up would be quite challenging. Someone has to try though.
1) I want to facilitate dialogue between influencers and followers, not dialogue between friends. You don't need thumb-ups/downs for the later: there's not enough interest to justify that.
2) I don't want to create another social network, and there's little chance influencers sign up here anyway. Hopefully letting influencers engage through their established channels make things easier for them.
It has some benefits for influencers to adopt it. On twitter, instagram, and youtube, the comment section is quite messy. If you're a big name, you'll be overwhelmed by questions, and same questions are asked over and over again. Going through all those questions to pick out important ones is tedious. This is basically a zendesk for them (if they want to engage with their followers). So you're right, like AMA, going from influencers' side probably has a better chance to bring the community up.
On the other hand, the fact that an important questions getting large number of thumb-ups is a statement by itself. Imagine a question for POTUS with 10k thumb-ups but got no answer from him/her. It's a headline material.
Yes, and this also brings other benefits. 1) They don't need to provide proof, as they tweet the answer from their official account. 2) They keep the engagement with their audiences in their established channels (I plan to add youtube in future too).