I'll be interested to see how a Twitter mode could work alongside the longer posts.

I think there's an audience for everything, might be interesting for some people.

I think posting rate should be related to your reputation.

Reputation is a vanity metric. Its usage on Steemit is purely frontend based (it hides the posts from the site, but they are visible on the blockchain). I think something more alongside the bandwidth algorithm already in place would be more suitable.