Lets say email didn't exist, and instead it came out today, do you think there's a chance in hell it would succeed? Everything in the early days of the internet was difficult in one way or another. Trying to get grandma's AT string right so the modem wouldn't drop at 24000bps and getting the POP3 server was configured was a nightmare. It mostly got easier for the masses when webmail became a thing. But again, I think it would fall on its face if introduced now.
First, it's important to define the metric for success. I would argue that Mastodon is already successful. It's a network that has over a million users on it, and that's growing steadily.
At this point, Mastodon will be around indefinitely, and it will probably outlive every commercial network that exists today. The only thing it needs to stay alive is to have enough users who generate content and run servers, as well as people who are willing to work on the code.
This is the core difference between open source projects and commercial companies. A company has to be able to produce profit, and a large publicly traded company has keep investors happy. Mastodon doesn't need to do any of these things.
