I do believe Twitter isn't doing well at fighting spam, also that it's a pretty hard problem. But where do you think people will go after leaving Twitter? Is there an option?
Does it matter where they'll go? People will always find some spot on the internet to have conversations after a given platform hits the friction threshold, and some might not even go anywhere: They might just leave.
Where people will go doesn't really matter, because there are a billion places they can, and there's not always a clear migration path. Sometimes, a social platform just dies, and its communities form a diaspora on different platforms, without any "clear" successor (like what happened to Orkut), or just stop doing the whole social media thing (many Google+ contributors no longer post online anywhere).
My question was kinda selfish. I want to move now. If there are a billion places, please tell me so I can move there now before the masses arrive and even that gets ruined :)
There's no easy answer to this. A billion different places users could go doesn't mean they have active communities, and if I mentioned where I like to hang out on the internet, those areas would probably get ruined.
Instead, I'll mention two platforms some of my friends like, to avoid taking the cost of a ruined platform myself:
sqwok.im: This one is the most microblog-like of the two, but it's also the least conventional. The quality varies; the front page only looks good every once in a while.
tildes.net: This one is invite-only, which helps mitigate the masses jumping in somewhat, and is run by a former reddit administrator. The existing community isn't great, but it's good. Friendly enough people.
