Until now I felt that Twitter was too big for Musk to really push people to a competitor, once there's a social media platform that everyone is on it's really difficult to get them to move elsewhere without offering something new. It's getting to the point however where a clone of the site might actually be able to take off as people move away from Twitter in protest in large enough numbers to gain a foothold and offer some genuine competition.
There are still a bunch of ways that Twitter can be improved upon too; account 'reputation', a landing page for each account to essentially provide a website within a website, better automatic moderation, a user-driven moderation system, better payment models, etc.
