Of course, ads are always a possibility, but being Open Source and having an open API, means that users can use any app they want, including apps without ads.
Basically if servers will post ads, then users will have the choice to view those ads as means of supporting that server, but not as something enforced at them by the server.
How does federation solve the problem of powermods?
It's possible to become a mod for a remote community outside your instance. I don't think anything technical about lemmy or the fediverse prohibits someone from attempting to become a powermod by founding or offering to help moderate many lemmy communities. I'd hope it doesn't happen again just from the knowledge of how it worked out last time, and that existing mods would refuse to take on mods with an excessive list of existing communities they moderate. But I don't see how federation structurally prevents it from happening again.
The thing about the Fediverse is that users own their data and can easily switch to an equivalent /c/
Also there's not one community for cats, funny, videos, etc. and having many instances moderated by different people means its more likely that the server admins will notice the "power grab" and return it to the hands of users.
This also solves the problem of power mods censoring users or blocking them across different subreddits, even though they have only violated the rules of one subreddit.
I'm much less convinced that that these things are meaningfully different in the fediverse:
It's as easy to shift subreddits as to shift lemmy communities. Self-hosting and "owning your data" doesn't really factor into the effort required to migrate a userbase to a new community.
Reddit has duplicate communities as well. Lemmy is exploding in usage right now and there's a lot of uncoordinated duplicates happening right now, but it seems fairly likely things will consolidate in short order as functionally unmoderated communities drift away from their topic and well-moderated ones accumulate posts and users.
Lemmy mods of multiple communities could block someone on all of them as easily as blocking someone on one, though the modlogs WOULD leave an audit trail of that action so compiling evidence of poor moderation is at least structurally easier.
We don't see powermods right now, and I hope we don't in the future. But if we don't, I think that will be mostly due to cultural factors rather than federation itself. Though as noted the modlog is a powerful tool to expose bad mods generally, irrespective of how many communities they moderate.
How so? I mean... It's only natural that the top 100 communities are hosted on 3 or 4 of the most popular servers. A mod that's power hungry enough to "moderate" 100 different communities isn't going to be tripped up by needing to create 3 or 4 different accounts.
By all means, I recognize that it's a problem, but I don't see how the fediverse offers a solution.