This is just an uninformed take, and I don't want to give the idea I know what I'm saying:

Probably very hard for things beyond the most basic browsing within one instance. There's unavoidable interoperability features we would want here but have no equivalent in a reddit environment, and such apps would just feel too limited versus using a browser with the current Web UI. For example, a user posts from another instance and you click to check their posts, which turns out are all over the place in federated space. Even if we create an API layer that condenses all those requests to a simple single call we would do on Reddit, how to label those results for wherethey reside is still another small UI headache. And that's one problem view out of a couple dozen in the app, while merely assuming single-instance browsing.

But more drastically, Lemmy's moderation tools are probably heavily different from those on reddit. Even if they're similar in actions - they're absolutely going to be dissimilar in completeness, Reddit is much older than Lemmy and has that time advantage. I know a large part of people who moderate reddit did it using third party apps for ease of use on a phone, and that's a demographic that probably can't be captured very easily.

Probably very difficult as reddit is easily a decade ahead of Lemmy.

It'd probably make more sense for the apps to adopt a plugin system whereby "fourth-party" developers can create add-ons for rif to access Lemmy, or bacon-reader to access mastodon, or reddplanet to access Facebook or Imgur.

This takes a lot of the load off the main third-party devs, and give the end-users a choice of using their favorite app with their service of choice, while keeping the apps themselves streamlined.