Hi, chiming in as a person from Mastodon from the past 7 years.
The rake in the grass that Feddit UK is going to run into is Transphobia.
FedditUK says in its rules that it wont allow Transphobia in its communities, fair enough, if thats truly what they mean great.
But this is the same rake in the grass that many of the newer instances over on mastodon since Musk took over twitter have run into, many of the journalism instances for example had strong "No Transphobia" rules, right up until a Telegraph journalist that was a user on their instance posted a transphobic article at which point the mods suddenly felt they simply couldnt restrict the free speech of a journalist even though it directly contradicted their own server rules.
The firm "No racism, no transphobia, no homophobia, no casteism" of the federation is pretty strict on that and many new comers to the fediverse find it shocking how "i just want to debate your right to use the toilet" isnt allowed on federated instances. And remaining connected to the greater federation requires that social contract and showing you're actually moderating and removing bad actors from your instance and blocking bad faith instances to protect your users and users of other federated instances who may use your communities/magazines/subfeddits for discussion.
The giant federation that agrees to these rules thrive as a big hub network, but theres thousands of tiny instances out there that dont that are defederated for very good reason (loli, gore, terrorism material that is illegal to own/view in the UK), a dark side to the fediverse ocean which is often joking referred to by mods as the "c*m" side of the federation (due to the sheer staggering amount of tiny 1-5 people instances with that word in its url), that includes places like gab, truthsocial, spinsterdotxyz (anti-trans subreddit), and so on.
lemmy federates with mastodon and pleroma, which means its open to all the above instances, theres gonna be a ton of instances that lemmy instances need to block to keep their users safe from spam and illegal content.
But after that, the question still remains, what are the admin or moderators of any of the FedditUK communities going to do when the transphobia rake appears in front of them?