Simply create a charge for each tweet.
And if people had to pay they wouldn't send out so much rubbish!!!
One step better, send ALL the money to good causes, in fact that would be the USP for a platform that wanted to compete.
50 billion tweets @ 5p each = £2.5billion
Have a lovely Sunday, I'm cooking Roast Chicken - you're welcome to come over (but please call first!!!)