If I owned twitter, I'd make the following changes:
-Install a profit sharing program for content creators that make videos and images.
-Install a feature that'll allow users to sell tweets instead of their users using other services to do this.
-Allow news companies and the government to purchase a notice all across the service for millions - per week? Per month? This depends on what the alert is about.
-Allow rappers and entertainers to stream a concert live. Yes, this will be a charged feature. So, this feature can cost an entertainer $5k-$300k for a 20min-40min set. This depends on their budget though.
-Allow users to see what their friends are tweeting about. It's hard to find tweets because of the mass volume of tweets. It's annoying sometimes. So, therefore, if you retweet or like your follower's tweets a lot, their tweets will show up first on your timeline.
-Implement social media sharing buttons for every tweet and trending topic. There's a lot of news stations that use twitter already, but they're not helping them grow at all.
-Allow content creators and company owners to post longer tweets for a set price.