The saddest thing about Twitter's path is that the tool is so good, but if they don't fix the problem you just described (brilliantly btw), they can be doomed.
I think if something the size of twitter failed, the loss of trust in a similar service's sustainability would prevent a clone from seeing critical mass for a long time, if ever.
edit: why the downvote? If you disagree, let's talk about it.
I hear your point, but what becomes the goto place for live events on the internet? Does a company with an established brand (like Google) attempt to step in with its own clone service?
I just can't see this form going away. A public-by-default, one-to-many microblog service has proven to be valued by a substantial userbase.
I have to think that the "next Twitter" could disguise itself as a sufficiently fresh take in order to gain enough trust from enough users.
Joking aside, I wish there were some meaningful numbers around how many people (as a percentage of active user base) use it that way (live events) vs just seeing what their friends and/or favorite celebrities have to say.
All it takes is a critical mass of users to migrate to a clone, (which I assume is very likely if the company were to fail).