Well, mastodon is completely open source, so it's more of a question of: "Which social media giant will shamelessly copy over mastodon's code and try to beat them at their own game."

This is the correct answer to OP's article title. Any social network that looks viable will be killed in its cradle* or integrated into one of the big boys.

* of course I mean acquired

There isn't really a "them" to buy. It's open source, and there are lots of instances. As it currently stands, if one instance sells to a company, I suspect the vast majority of people will migrate to other instances.

Indeed, I expect that a migration tool will be developed soon for exactly that reason - it's exactly the paranoia-inducing scenario that will provoke the type of person who runs an instance.

I certainly wouldn't sell my instance.

none of them. mastodon is not innovative from a UX or business model perspective, it's an explicitly derivative product meant to be like Twitter. there is already a Twitter and it is already not much of a threat to other social networks.

the innovations in mastodon are how the network is administrated and (arguably) the differences in culture that network federation creates as an alternative to a centralized platform. those innovations can't be copied or bought by a company already committed to centralized administration, which is almost certainly a compulsory thing for a for-profit business.

There's nothing to buy... it's a bunch of servers run by individuals.