On the other hand, a Twitter-hosted URL shortener would add long-term stability to links. If Twitter is handling the shortened URLs, you know those links in your feed will stick around for as long as Twitter does.

For similar reasons, I don't see much harm in custom shortened URLs. If major players like Amazon, the New York Times (nyti.ms) and the Huffington Post (huff.to) are all paying to use bitly.pro, it's unlikely those links will die, and bit.ly becomes a more viable business in the process.

The question is whether Twitter's URL shortener is on a crash course with Web sites who'd rather use their own custom shortened URLs. They need to reach a compromise, lest URL shortening business get any messier.