The account portability is probably the biggest problem with the fediverse right now.
I finally signed up for Mastodon despite reading little to nothing positive about it on hn. It was easy to use, and the signal to noise ratio was vastly improved from my Twitter experience.
However, that lack of account portability means users can, have, and will continue to get cut off. Servers cost thousands of USD per months with no revenue and domain name ownership can magically vanish for many reasons. With no business model for server operators, these are significant issues.
That confusion for users may even be the primary force that drives them over to something like Facebook's Threads.
There are analogies to e-mail here for the server operator. If I said any numbers I would be making them up, but I'm assuming 1 Mastodon user costs a lot more, both in compute/bandwidth and support, than 1 e-mail user. Free servers are not going to scale.
Account portability doesn't solve this, but it means if something happens to one server operator, that user doesn't churn in to the ether and never return. I've been keeping an eye on https://fedidb.org/ (not my site.) While total users and servers keep going up over the past year, active users keep dropping. It could be something related to how they record usage, but it isn't a promising thing.
I'm less skeptical about long term adaptation. Most of the negative sentiment I've read on hn about Mastodon just was wrong. Facebook, Twitter, Apple, Microsoft are all fully accelerating in to ad business models which will make much of their products less unappealing by the day. If history is any lesson, when a new competitor shows up without ads and a similar or better experience, the incumbent is in trouble.