I can only see Mastodon centralizing to cope with the load. But a server going down on this load from HN tells us it is no where near ready to handle an insurmountable amount of users or even begin to challenge Twitter which hosts 220M+ users every single day.
https://pagespeed.web.dev/analysis/https-twitter-com-realDon...
Mastodon.social is actually much faster on this particular benchmark. So maybe there is hope.