@tomw I see what you're saying, but it's equally true that the opposite may be the case. Even though they don't intend to, lots of new users may have the effect of centralising Mastodon.
Yes, yes. I know about the decentralised architecture, open source, blah, blah. But a huge number of users constitute a huge market, and that'll attract someone, somewhere to create a value-added layer to Mastodon that'll have the EFFECT of centralising it.
I reckon data-mining may be the mechanism.
@jameswallbank I can imagine a "super-instance" emerging that would have some of these effects – think for example of what Gmail is to the email world. But it is still possible, at least, for other email servers to send and receive from Gmail (most of the time).