I can see the use case if it's a extremely short edit window.. something like 30-60s, basically to catch that stupid typo. That doesn't solve the abuse angles but it gives a much smaller opportunity for it to happen.

Short of [mega star], few tweets see much favoriting/RTing in that window.

Exactly! I'd say I am strongly against the ability to edit tweets. I'd even put it higher than the strict reverse chronological flow of tweets that I prize so much that I still allow Twitter to send me tweets by SMS.