Unlike GitHub, tweets should not be editable forever. I think 5 minutes is reasonable. Even HN has an edit time limit. I hope they also limit how much you can tweets (even though, in reality, adding 4 characters (“not ”) is destructive enough.
I kinda wish they let people add some text instead of allowing editing, like:
Wouldnt it be nice?
Added: * wouldn’t
Maybe if you're a famous celebrity etc. but it's scraped mine 5 times since 2007 (and the "expand conversation" links don't work) and I promise you that it has been fairly active ever since I signed up.
Discussion forums have had edits forever; reddit famously lets you go and delete all your existing posts at anytime by replacing them with "edited by autodeleter9000".
Links and uploaded media should not be editable.