Oh BTW, the Cinny web client for Matrix does a very good job replicating the general layout of Discord without being an outright clone. There’s even a feature to “Categorize Subspaces” that lets you precisely replicate the server/category/channel structure of Discord using Matrix spaces.

insert that clip of Michael Scott from the Office shouting various varieties of “No!” here

If the discussions I see on Mastodon are anything to go by, then the moment people find out that your hypothetical future instance shows ads to its users, they will embargo you by blocking all communication with it.

And hiding that would be impossible: since Lemmy uses the AGPL license for its source code, when you add the advertisement code to it, you’ll legally have to publish the changed source code, at which point people will be able to find out what exactly you did to it.

P.S.: also, the possibility of doing that (or even just collecting and selling data) is exactly why a lot of fediverse users distrust large instances like mastodon.social, to the point that these also get preemptively blocked (though also that one specifically is said to inadequately moderate the posts people put out, as the spam-bot incident has shown, so there’s more than one reason to do so)