Twitter's usefulness mostly comes from the celebrities being there. The initial reason the celebrities were attracted probably had to do with the char limit, its pretext, that they are not expected to read too much and that they are not expected to write too much.

You'll see on reddit - at least, back when these things were being determined - a lot of celebrities, when they did AMAs, seemed to feel obligated to respond to every comment with a comment of similar length. Sometimes they wouldn't wait and see which comments were getting the most votes and answer those, they'd just start with the first one that hit their mailbox and work down the list until they ran out of time. My guess is, non internet-native extroverts really needed a platform that would advise them about what's expected and reasonable.

But I think, now that we're all learning that we must moderate our consumption, the celebrities (and most other people) remain on twitter mainly because the celebrities were there in the first place. I don't think we need the char limit any more. I think maybe we're ready for the training wheels to come off.

But there's another reason redditlikes don't really work for a general audience. Mainly specifics about how voting tends to work. There is no accommodation of subjectivity. Everyone sees the same vote ranking even though different people have different interests and standards. The problem is partially mitigated by separating people into different subreddits, but eventually, general subreddits like /r/worldnews, /r/technology, /r/science or even /r/futurism will grow large enough and diverse enough that people wont be able to stand being around each other again. Every demographic other than the largest, most vote-happy one will have to leave. I really want everyone to be able to join together in the same conversation, but when the top-ranked comments always turn out to be "[outgroup lies]" or "[childish inanity]", that can't happen. The outgroup wants to see their lies, and the children want to see their inanity, and I think they should be able to, but good adults need to be able to hear each other too, or else they'll just move to GoodAdultSite and then the outgroup wont be able to find refutations of their lies even when they look for them, and the children will not receive the advice they need even when they call out for it.

(I have some ideas as to how to build a redditlike that might solve this. If anyone's interested, speak up.)