A single app that would be able to show all federated social media content like lemmy,kbin, Mastodon, pixelfed, misskey and perhaps even the coding ones too ( each repo could have a lemmy like community for help, news, updates,etc). Imagine if it only required a single account to interact with all these platforms.
IMO, its a more logical approche to the Fediverse. All platforms easily accessible and intractable with a single app. The burdens to the app developer would be huge but it would revolutionize social media forever.